How large, what scale?
If you want to be simple about it, get some thin clear plastic, and many many sheets of styrene. Some cutting tools, putty, glue, and paint. And your good to go. Most modern buildings are simply square sky scrapers, could easy replicate them.
Put a sheet of clear plastic, then use strips of thin styrene to simulate the window frames (for those all glass ones) That kind of thing, but then, I may just be a raving crackpot who has no idea what hes talking about, I do build giant robots afteral