T he nation’s top builders are more than just real estate developers or contractors. They’re engineers and architects, sometimes of literal physical infrastructure, and sometimes of the intangible networks of computing or capital. They are entrepreneurs and leaders who have built companies and systems, often from scratch, that have not only endured but that have created lasting value for their customers, employees and families.

Over the years, Forbes has spoken with several of the honorees of our Builder 250 list , which honors some of the greatest living examples of creating an enduring legacy—our generation’s answer to the impressive likes of Rockefeller, Carnegie and Morgan. Each of them has their own principles for scaling and building a business that is a financial success for years to come.

WARREN BUFETT Former CEO of Berkshire Hathaway

Net Worth: $141.5 billion

Warren Buffett began building wealth very early on. As a precocious seven-year-old, he read “One Thousand Ways to Make $1,000” and started selling Coca-Cola, gum and magazines door-to-door. He made his first trade at 11, buying three shares of Cities Service preferred stock for $114.75. Over the eight decades that have followed, Buffett has built his legacy as perhaps the greatest investor of all time, thanks to one core principle: Invest in things that last.

“[My] strategy is to find a good business—and one that I can understand why it’s good—with a durable, competitive advantage, run by able and honest people, and available at a price that makes sense,” Buffett once told Forbes . “Because we’re not going to sell the business, we don’t need something with earnings that go up the next month or the next quarter; we need something that will earn more money 10 and 20 and 30 years from now.”

He has steered Berkshire Hathaway—which he took control of in 1965, when it was a small, struggling textile manufacturer—into long-term bets on insurers, electricity providers and railways. Its Acme Brick Company churns out around 1 billion bricks per year; its Duracell batteries power the nation’s gadgets; its Fruit of the Loom sells underwear, t-shirts and socks in 80 countries. Today, $1.3 trillion (assets) Berkshire Hathaway owns hundreds of businesses, plus huge stakes in publicly listed companies such as Apple, American Express and Chevron.

““[My] strategy is to find a good business—and one that I can understand why it’s good—run by able and honest people, and available at a price that makes sense.”

All this has built plenty of wealth for Buffett (who is worth an estimated $141.5 billion , even after having given away roughly $73 billion), early backers such as Stewart Horejsi ($4.1 billion), current CEO Greg Abel ($1 billion)—and millions of shareholders who have ridden Berkshire’s 6,000,000% stock price return since 1965.

Even more important, though, is how Buffett has taken his buy-and-hold philosophy to the masses, convincing scores of investors from Wall Street to Main Street to think more about the long haul than short-term market movements. “In the short run, the market is a voting machine,” he likes to say. “But in the long run, it is a weighing machine.”

MIKE HOLLINGSHEAD Founder and Chairman of Smyrna Ready Mix

Mike Hollingshead knows what it’s like to build something from nothing. The 56-year-old founder of concrete maker Smyrna Ready Mix (SRM) grew up in a Tennessee trailer and struck out on his own in the concrete business at the age of 20. Last year, that business brought in $3.5 billion in revenue.

The origin of that success goes back to the people he met along the way. He went to work as a concrete finisher at age 18 after meeting his first boss at a local bar the night before. When his boss moved away, he gave Hollingshead a list of customers whose jobs needed finishing, which in turn allowed him to start his first business. When Hollingshead decided to make his own ready mix concrete, it was a banker in town who stepped up with early loans to fund a plant in his backyard and five heavily used concrete trucks. And when his drinking got in the way of his success, his wife gave him a path forward via their church, and an ultimatum. Today SRM has more than 8,500 employees, and Hollingshead considers them, not the concrete, his most important resource. “If you take care of your people, give them opportunities, and provide the support they need to succeed, they will take care of the company and its customers,” he says.

“If we ask people to dedicate their careers to helping us build this company, we have a responsibility to invest in their lives and their futures.”

A major part of that is ensuring that employees share in SRM’s success through pay, benefits and growth opportunities. “If we ask people to dedicate their careers to helping us build this company, we have a responsibility to invest in their lives and their futures,” he adds.

The tougher the times, the bigger responsibility the company has to its employees, customers and communities. “We have always tried to make decisions with the next generation, and really the next 100 years, in mind,” he explains, noting that even the quality of materials used is a reflection of those values because they are an integral part of the high-rises, bridges, roads, schools, hospitals, churches, homes and other structures that people rely on every day.

To Hollingshead, building isn’t about the physical structures. As he says, “It is about building people, strengthening communities, and leaving behind something that will continue serving others for generations.”

Data centers may be the headline trend thanks to the AI boom, but they’re nothing new to Bob Clark. The CEO of construction company Clayco has been building them since the 1990s–which back then usually meant installing some computers in an existing site. Today, the 67-year-old is building what amounts to self-contained cities housing thousands of machines, some of which have their own power and water supplies.

One key to building at this scale is modularity. Clayco builds components for data centers to its own designs in a factory setting, then ships them where they need to go rather than building on site. It’s a process that efficiently makes use of the company’s 50,000 full- and part-time employees who are currently working on around 100 projects across the country. It goes beyond its own staffers to its coordination with its many partners throughout the design, engineering, funding stages to the multitude of assignments on the worksite.

Another key is both market and geographic diversification: Clayco doesn’t just build data centers. It’s also constructing electric truck factories for California-based Rivian in Georgia and Illinois, and recently completed the Obama Presidential Center in Chicago. Clayco pulled in $12 billion in revenue last year, which Clark in part credits to its culture of collaboration. “A shared strategy, open book managed business and sharing the wealth has been our plan from the beginning,” he says.

“I don’t believe in generational wealth giving. I’m not going to make my great-grandchildren billionaires or millionaires before they’re even born.”

Beyond the usual benefits, which of course it offers, Clark eventually intends for Clayco to belong to its employees. His CFO and key executives already own about 40% of the company, and he says he intends to distribute nearly all of the rest to employees. “I don’t believe in generational wealth giving,” he says. “I’m not going to make my great-grandchildren billionaires or millionaires before they’re even born.”

That said, he has helped his children build their own future. His son, Shawn, runs CRG, Clayco’s real estate development company, which has $500 million in assets. And Todd Weaver, who Clark and wife Ellen “adopted” as a mentee as a teenager, now operates his own construction empire , DGN Enterprise, which has nearly $1 billion in annual revenue building for the likes of Google, Apple and Microsoft. Says Clark, “We build to make life better! It’s a true part of our culture.”

DON’T BE AFRAID TO REBUILD

DANIEL GILBERT Founder, Rocket Mortgage

Sometimes building is about rebuilding–something few people might know better than Dan Gilbert. In 1985, with $5,000 he made selling pizzas, he founded Rock Financial, today known as Rocket Mortgage. He sold the company for $582 million to Intuit in 1999. Three years later he bought it back–for $64 million–and has rebuilt it.

Along the way, he reinvented the way mortgages were done. In 1998, he made the decision to move the mortgage business online, closing down physical branches and opening up its first website within a year. That allowed him to speed up the process and build a national platform that could do lending in 50 states, which made it much more convenient for customers.

Today, Rocket Mortgage services more than 10 million families every month and has closed more than $2.1 trillion in home loans, making it the biggest mortgage lender in the country in terms of number of loans originated. Among those with loans are its own employees who get exclusive mortgage prices and down payment assistance.

None of this is an accident: Gilbert has an explicit philosophy for running his company, based on 16 principles called “ISMs.” One that’s particularly applicable to rebuilding, or better yet, reinvention, is the company’s obsession with its never-ending quest to find a better way. That’s why it took three years for more than 500 developers, designers, QA experts and business analysts to create the digital experience that is Rocket Mortgage today.

His company isn’t the only thing that he’s rebuilt. For more than a decade, he’s been focused on rejuvenating Detroit and Cleveland. Through his companies and foundation, Gilbert has committed over $9.2 billion to this effort, which has resulted in the development or restoration of over 127 properties. Additionally, he made sure $15 million went to cover property tax debt owed by around 20,000 low-income homeowners and $10 million for local startup founders.

It’s an effort that hasn’t just revitalized the area, it’s also brought thousands of workers into downtown areas, helping his companies thrive. When he began the project, he had plenty of doubters, but for Gilbert, it was a necessary leap of faith. “Everything we’re doing down here is based on the concept of not measuring things,” he explained to Forbes a dozen years ago when work was just getting underway, “We believe in the long run we’ll create a lot of wealth from all this. But it requires a major league belief in doing the right things.” No doubt it’s paid off in multiple ways.

Additional reporting by Matt Durot and Chris Helman , Forbes Staff