This is admittedly a bit lame and probably already suggested, but if you could move buildings once built it would allow you to create/group buildings together in cool patterns, like types, etc. Probably just my OCD talking but I like to have the build layout look cool. I've also re-built my HL like 50times...
Would be nice to move. Would be better if you would get stat boosts from arranging them in the most effective ways also. Like have lookout towers on the corners, attk bldgs on parameter etc. That would make it worth wild.