What Milo said above gets my vote; it's what I have done in my situation (WAP installed in the remote building with it's own wifi regime back to the main wireless/modem/router) . The effectiveness of the wireless link can be enhanced by using antennae with directional characteristics where this is convenient and practical. Happily I was able to operate with strategically placed omnidirectional antennas, and very short lengths of RF cabling.