Depends on whether you want a permanent solution or not and what your budget is like. For that size I'd say try using just one wall painted green or use fabric. The height is of concern - 7-1/2 feet is tough because your shots are limited to head-on unless you want to paint the ceiling and floor, but then you may want to look into getting some styrofoam and making an infinity wall and soundproofing the ceiling. The options just keep growing. Cowboy studios on amazon has some good temp options (large 10'x20' green screen fabric) as does tubetape.com. Shop around and find something to suit your budget and leave room for lights (light green screen separate from talent), soundproofing, camera in various positions, talent, props, etc. consider your workflow in terms of your software, too - how to pull your mattes efficiently will be driven by your setup.
We converted a 2 car garage into a 2 1/2 walled green room with all rounded corners, separate lighting for the walls, soundproofing, etc. it cost a small fortune, but it was worth it. Your eyes get funny with that much green too! ;)
Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293