I made the 8 ft straight bar with a double tap keggerator and made it from solid oak, tile, glass and mirror. As it turned out the thing wound up weighing estimated over 600 lbs (3/4 thick oak plywood is heavy!) I originally planned on having casters on my bar so I could move it ouside to the deck for parties.
About casters, first of all, do not forget that the caster on the bottom will make your bar top higher – like up to 4″ (not a big deal for a regular bar, but for kegger bar, you need all the space you can get inside). I talked to a lot of people regarding casters as well. The other thing about wheels is that with the weight, you will want soft, large wheels. Tiny wheels will have trouble rolling over bumps (like spaces between the deck boards) and hard wheels might make permanant marks in wood, or crack tile. My recommendation is if you are doing a regular bar then get as large and sturdy casters as you can fit under it. For a kegger bar or a heavy regular bar, I’d suggest skipping casters and simply use some 2″ schedule 40 or 80 (as thick as you can get at home depot) PVC pipes – it can be rolled around like a breeze on a couple of those.
I just wound up forgetting about casters on my bar and had to get a small army of people (10) to move it into the house. Even with as heavy as it is, it still moved easy, even across the yard on a couple PVC pipes