SAN DIEGO – First came home offices where new ideas turned into a small business.

Then Starbucks became the place to work on a laptop and network with neighbors and clients.

Now a new concept — "co-working" or "shared workplaces" — is taking hold: Rent a desk for $500 per month in a warehouse or commercial building and work alongside other entrepreneurial "soloprenenurs."

The sharing economy has produced this growing type of office around the country to the point where an estimated 40 percent of companies are thinking about adopting it in some form themselves.

"This is perfect — exactly what we were looking for," said Ryan Johnson, 24.

He's one of five venture-capitalists at Israel-based OurCrowd, who work at DeskHub, a 15,000-square-foot co-working space in San Diego.

He previously operated out of his apartment and now is able to invite dozens of angel investors to monthly meetings. Once in a while he picks up tips from other DeskHub companies for possible investment opportunities.

"We love the ability to network with other entrepreneurs and start-ups," Johnson said. "There are days when the main room at lunch is just crazy — people having conversations, people touring around. It's a cool environment. You're always talking to somebody new. I hear people making connections and introductions I'm sure they would not have found if they weren't at DeskHub."

Jay Chernikoff, 36, started DeskHub in Scotts­dale, Ariz., almost two years ago, when he was shifting from tech to real estate and needed a flexible workspace.

"The idea is as companies grow and become bigger or smaller, they want to retain flexibility," Chernikoff said. "It's the same as the 'rental' economy, Uber, all those things. You have offices shifting in that way, too."

The CBRE brokerage began publishing special reports in January on the shared-workplace movement. It found the commercial real estate world is taking notice, partly in reaction to rising real estate costs in urban centers, the very places where many millennials, the industry's future tenants and customers, want to live and work.

The brokerage also said office-based companies see co-working as a way to gain more efficiency by using less space per person.

In San Diego CBRE broker Evan Knudson identified 11 co-work spaces in 18 locations that add up to 109,047 square feet. While a typical office plans for 250 square feet per person, a co-work setup can reduce that figure to as little as 66 square feet.

That's because there are no file cabinets, closed-door executive offices and duplicate bathrooms, break rooms and conference spaces.

Co-working spaces can attract some interesting and imaginative businesses.

Wag! is a dog-walking service. 6 Degrees is a meeting organizer. GreekRush develops software to help fraternities and sororities organize and manage their rush periods, events and routine business.