Serial entrepreneur Kevin Ryan is know for leading DoubleClick to its $1.1 billion acquisition in 2005. He also co-founded MongoDB, Gilt, Business Insider, and Zola. As such, Ryan knows a bit about building offices to keep thousands of employees happy and productive.

Currently, his companies have more than 2,000 collective employees, though he notes that will very soon be a smaller number, due to the recent sale of Business Insider to Axel Springer. ("I'm pretty sad about it, but it was a pretty compelling transaction," he said.)

Thursday, he took the stage at Techweek to talk about office design. Starting in 1985, he said, he started one of his first jobs working at Prudential. "It was in a really, really ugly office," he said, typical of the Office Space era with crammed-together cubicles surrounded by executive offices. By the early 90s, he was designing his first office, as the COO for a company with about 150 people. He actually laid out the space with individual offices for individual people. And zero flexibility. That was a mistake, he quickly learned.

By the time he was at DoubleClick in the 90s, where the staff rapidly grew from 20 to 2,000 employees, he saw the error: "Employees were moving every two or three months. There I realized I had to have space that was flexible. People need to move."

Step four was designing the Gilt office. Of utmost importance is the heart of the space. "You want to have a central area that is beautiful and reflects who you are as a company."

And gone are those executive offices. In fact, he said, at Gilt there are no private offices whatsoever. "I don't have an office--I have a standing desk that looks a lot like this [podium]."

To be clear, Ryan said, despite all of the influence Google and Yahoo have had on office design, designing a startup workspace isn't about making it look like a college campus or gaming room.

"It's not about ping pong tables," he said, though he admitted he loves a good ping pong table. "It's about having a comfortable place people feel good in."

And that idea of a comfortable place is one that includes flexible conference rooms, meeting areas, and collaboration space. Even the big guys, say, like his old Prudential, are getting in on that startup-office inspired trend.

"Tech is dominating the aesthetic in office design across the country," he said.