If you can, cut a pit with a demo saw and do a full downdraft. Tile floors, wet filter.
It all depends on how much polishing you are going to do. If you restore 1-3 cars a year and seldom use the finish out of the gun on the final product, meaning you want insanely smooth wet sanded finishes, a cross draft will do. Even outdoors will do or a vinyl curtain make-shift bay with exit and entrance filters will work.
If you cross draft, go loooong. You don't want the car anywhere near the entrance filters and get good at being very patient and vigilant with tack cloths (I use 3-4 per car, per complete job) and some 600 paper to nib basecoats, on anything that takes more than 5 base color coats to cover.
The idea is to keep the entire environment super clean, including the car and keep the air flow clean. Always mask window openings and skirt the car down to the floor with paper, taped to the floor. If you go cross draft, make sure the dead spots on the car with the air get extra attention on tack cloth and nibbing. It also helps to park the car as aerodynamically as you can in the booth flow direction.
