There's not a lot of magic regarding projection room floorplans these days, but there are a few obvious guidelines.
You want your projector centered to the screen. The port (hole in the wall), where the projector shoots to the screen needs to be high and wide enough and the projector has to be physically high enough to shoot over the tops of passing cars. There are a lot of drive-ins with ground-floor booths, but I prefer a second-story room. Distance from the screen to the projector, as well as the screen size will dictate what lens you'll need. There are some restrictions here, so a visit to a theatre supply company (or two) will give you a lot of good information. While you're there, ask about the electrical requirements of the equipment you're considering. That will have to be added to the other needs of your concession & building operations.
As there are few other hard-and-fast rules, I would strongly recommend you visit a few drive-ins, well outside the area where you're interested in building. You might find their owners willing to let you tag along for a bit, and get some ideas for your own place.
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