One of our older orchid club members also has a greenhouse constructed in the basement of his new house. Up near the adirondacks, their climate is like sweden pretty cold. By using a preformed greenhouse structure, you don't have to use nails/screws or damage/alter the walls of the garage or basement, and if you do end up having space outdoors when removed it can be used again. It does a better job of keeping in the moisture, which could be bad if you have any wood or any porous surfaces in the basement/garage. Easier to put together a greenhouse from a kit, as long as the directions aren't in Mandarin (unless you speak it), than lining the whole inner surface of a room especially more so if it is a large room. Of course, you could hang pipes from the ceiling to drape clear plastic from, taped together that would hold in moisture and heat, but not look as cool or be as sturdy as mounting things on the walls/ceilings of the greenhouse (like fan tubes or exhaust vents)