Empty buildings? Forget that. My wife won't let me get a 40ft shipping trailer. Less than $3k here for WWT. 8'x40', I'd use 2' of grow space on each side, and leave 10ft for supplies/reservoirs at the front. That leaves a 4' walkway in the center, 30' long, 2' of plants on each side. Then here's the kicker, shelves. You heard me, shelves. 8' of height? Perfect, 2' wide shelf 4' high. Keep plants at 2' height and cob leds handle this perfectly. Now you've got 4 sections of 2'x30'x4' grow space, 240sq ft of grow space out of a 3k wind and water tight trailer.(and $8k in lighting(DIY)) Expect 1.5oz min per square foot, or 22 pounds per cycle.