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Any regular size garage, single car or two car space works really well with a halfpipe, either to fill the whole area, or just do quarters that can be moved / stood up if needed.
Did you mean to have things going diagonally across? That would give you a little more distance, but still pretty cramped for having any decent obstacles, but that doesn't mean it can't be done.
I recall seeing some street type setups where a guy has one push, hits a small ledge or rail or parking block, is able to do something and turn off before stopping at the end wall.
Building a small halfpipe can make a garage space way more interesting, even if you don't skate a lot of transition, something small enough and mellow enough can make it more worthwhile than a flat ground or small street space, but I can still skate the flat area of my own ramp often enough too.
My rational thinking with my shed ramp (equivalent of two car garage dimensions) is that I can skate a skatepark or street type spots a lot more anywhere else, but there are not a lot of nice small halfpipes around to skate. I also have a small ledge and a few other things in miniature scale that I can still get out and skate in the other side of the shed too, one push do something and roll a bit and stop. I can also take these out to the driveway if needed, or fit in the car too.
There are a good number of interesting pics online with garage skateboard ramps or similar things too, but really it is up to you with whatever you might enjoy the most.