Where and how much is the house?????
I'm building a new garage in the spring (my freakin' village dragged their feet approving it this fall, just got the permits), and have talked to several of the lift companies. Basically, you need a 5 inch slab for your standard 4 post lift. 4 inches is fine, but, it you are pouring it, might as well give yourself some wiggle room. Besides, most of the 4-posters are rated for up to 7000 pounds, most of the exotics / semi-exotics are well under 4000 lbs, so you would be well under the limits. BTW - sears is having a decent sale on the Craftsman cabinets.... just dropped a decent chunk of change for the cabinets for my unbuilt garage. I consider myself pessimistically optimistic about the project!
With all these great garage projects coming up, maybe we should have a bit of a competition next summer. I'm sure FOC could come up with a nice trophy for the coolest Garage Mahal.
In my opinion the 4 post lift is much more convienent than the 2 post for everyday use, easy drive on and off. As mentioned be sure if you are thinking about a 2 post that it will be able to get it under a low car. The 2 post will have twice the floor load of a 4 post, so be sure there is enough rebar in the cement to hold it. For simple wheel service I raise the 4 post lift to about 18 inches, slip jack stands under the frame points and lower the lift leaving the car supported by the jack stands - this is an easy no jacking method use of a lift!
I have always wondered how someone would use a 4 post for anything other than storage but I like your idea. Do they sell jack stand support sections or anything to raise the car on the 4 post with a wheel off? Thinking about it next year. Brian