My advice is to get a "Bunk" style and definite stay away from rollers!
If the guy has any savvy building trailers he should know how to set it up?
I had my trailer custom made for my 260 from a company here in Ontario and the guy did a fabulous job. Trailer towed very nice!
The front rest was moveable so you could set the tonge weight for a positive weight of a couple hundred pounds which is normal. You DON"T want a negative weight on the tonge or the trailer will sway all over the place on the road while towing.
The boat was very easy to load and I did it many times alone.......
Here are some pics of my trailer: