Having grown up around trailers, trucks, and vans (In addition to farming my dad ran a hauling service, which he does full time since retiring from farming) I have seen them all. Being a builder you are probably only moving a few pieces at once. So if you want something a small enclosed trailer with an 8' ceiling would be the best to buy. If you buy one with an aluminum frame it will outlast you if you maintain it.
But if it were me I would hire movers to deliver pieces. Say it costs $200 for them to deliver a piece. This may seem like a lot, but when you figure a trailer will cost about $5000 that's 25 deliveries. When you add in the cost of insurance for the trailer, registration, tires, brakes, repacking wheel bearings, etc. you are spending a lot for the trailer. If you buy a van those costs go up.
Plus a mover is a professional mover. You make furniture, he's probably no good at building furniture, why would you think your good at moving? He will have a large truck, dollies, carts, padding, experience, and most importantly insurance. If a piece is damaged while being moved and it takes you 10 hours to fix it, if you were moving it you eat those hours. If the mover does it he has insurance to pay you. Plus that great customer just turned into an ass because of the tiny nick in their paint and wants all the trim repainted.
If it were me, when ready to replace whatever your driving now, I would buy a pickup with a small V8 and put a cap on the bed. this will allow you to move small things that are a one man job (I'm thinking chair sized stuff). It will also allow you to pickup materials. Buying a V8 will allow you to rent a trailer for bringing thing to shows. If your in the city get a truck with a 6 1/2' bed otherwise the 8' bed is great for hauling. Get a tall cap, this will give you some flexibility in what you haul.
This of course is my opinion and worth twice what I'm charging!
-Tim