When my Dad built his house in 1962-3, he had one build in the garage under one bay. Concrete forms and floor for the pit, back fill for support, concrete floor in the garage. Most of the time, it was covered with two wooden covers he made from plywood. At some point in the last 10 or 15 years, he came up with some aluminum diamond plate. Much sturdier and less apt to rot when snow, slush and such drip on it. In and out was via an old wooden step ladder (three steps, including the top). Ventilation? Um, open the garage door and hope the vapors rise out. To my knowledge, only twice did someone manage to get a wheel in the pit; both times were a dip-**** boyfriend of my sister's. Back then, yeah, I guess it was legal. Now? No way.