Wow you have free rain to create a proper brewery there, i'd seal and paint the floor, buy in some stainless steel racking, run water in and fit a nice stainless steel sink into the work surface, fit a few power points, a nice stainless steel preparation bench and fit up a couple of larder size brew fridges side by side. In addition i'd fit some heating in, its a real chore being out there dead of winter, some halogen light tubes for lighting.
If its a real big garage then maybe fit a stud wall half way down and turn half into a pub, a small bar, pump your beer direct from your Corny keg to the bar, a few armchairs and a wide screen TV and you'll have yourself a real man cave :razz: