We build in an old warehouse owned by the county, which they've let us use under the umbrella group GEARS (Garrett Engineering and Robotics Society). We have over 5,000 sq ft total, with a large warehouse room big enough to house a full practice field and then some, with an alcove off in the corner holding our toolshelves and bench tools; a loft room holding computers, a white board, and chairs; and a front room that holds all our LEGOs, trophies, and our kitchen. Yep, kitchen. The only kitchen you're more likely to find a robot than food.
We're exceptionally lucky with our building space, not least because our next door neighbor is a machine shop and one of our partners.