Can't stress it enough.. pre-planning. So much. Figure out exactly how you're going to make it. Nothing sucks more than finishing and realizing.. "oh wait, I have no way to take this to the convention because I lack the right vehicle and I actually needed to have this abled to be disassembled into pieces.." And it's alot harder, and more work, to split an already done prop into pieces than to have it split at the very beginning. Make sure you're able to get through doors and go through elevators.. If that means you need to have your prop fold up or disassemble, then it's probably best to do it.
Also, make sure you have a sturdy base or core. Once you go past a certain size with props, gravity and laws tend to want to pick fights with you lol. Things that you could get away with with a small to medium sized prop, become amplified when you increase in size.