One of the most irritating obstacles encountered by growing startups is the hunt for affordable office space. Startups with a dozen employees generally aren’t interested in leasing vast tracts of space, which makes them unattractive clients for business realtors, so they’re typically left to fend for themselves.

Rofo, a new startup founded by two former commercial real estate brokers, is trying to offer small companies a solution. The site recently launched in public beta, and specializes in offering real estate listings for offices up to 5,000 sq feet. For the time being listings are restricted to the Bay Area, but the company hopes to expand to other regions in the near future.

Rofo (which stands for “Right of First Offer“) sports a basic but intuitive interface that allows users to specify the size of their desired office using sliders. Users can tag suitable candidates with the “shortlist” option, and each listing is plotted and pictured using integration with Google Maps and Microsoft Virtual Earth.

To generate its listings, the site crawls a number of partner commercial real estate sites for open office inventory, and also monitors XML feed from brokerage firms and larger landlords. Users can also create a traditional direct listing, similar to those seen on Craigslist (but hopefully with less spam).

CEO Alan Bernier acknowledges that there are some strong competitors in this space, including Loopnet, but points out that many of these require a fee to post or view listings. Conversely, Rofo is free for both brokers and browsers. As with other realty sites, Rofo’s success will lie in its ability to collect useful and current listings. Bernier says that the site currently has about 80% of the Bay Area market covered, but that number will be hard to maintain as the site expands to new areas.

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