The monetization of unused assets is hitting your spare closet.

Roost, a peer-to-peer marketplace for renting out your garage, attic and other storage spaces, is now entering the collaborative economy.

The idea was born when a relative came to town.

“My older brother moved to San Francisco from Austin last year,” CEO and cofounder Jon Gillon told VentureBeat. “He had a Subaru full of [his stuff], and, instead of renting storage, asked me to make room in my storage closet,” he recalled. “When he came back to pick up his stuff, a lightbulb went off.”

The lightbulb (not the one in the closet) was simply that “people could make some money, and save some money” by renting out extra space they or others have. When you start looking for it, space is all over the place. For instance, if you had possession of one, you could rent out a parking space.

“Theoretically,” Gillon said, “you could rent out your back pocket.” Although you’d have to work out, of course, the terms of storage when you change pants.

Theory aside, he said the smallest space to rent out “is probably [the space to store] a pair of skis,” and there’s a minimum payment of $5 a day. Roost takes 15 percent of the transaction.

He first tested out the marketplace idea on Craigslist and TaskRabbit, with Gillon posting that he had some boxes to store. He found “a great response on TaskRabbit,” he said, where people undergo background checks.

But Roost (not to be confused with another Roost startup) will be providing tools specifically for storage needs. It has search filters for access, size and storage type, plus insurance coverage, safety guidelines, best practices, and support. Hosts’ profile information, public reviews and ratings are available, and a private messaging system enables users to iron out details.

The background checks, from Sterling Information Systems, are not yet available on the site, but they are expected to be within a month. “You don’t want to store your stuff with someone with a criminal record,” Gillon observed.

Of course, when you rent out space for things someone else wants to — you know — hide away, there are all kinds of possibilities. Which is why Roost offers insurance, and ways to check out the other person.

Two seed rounds have been raised from angel investors, of $135,000 and $160,000, and the current valuation “is about $10 million.”

“Now there’s an incentive to declutter,” Gillon pointed out.