You need to give them a few measurements. These are some they will definitely need. I am not sure if this is all of them tho. These are the details I used when ordering trailers.
Distance Bow Eye to Transom
Length Over All
Weight Loaded with gear and fuel
Hull Type and Make/Model
Engine (outboard, I/O, Inboard,)
Keel or no keel
Bunk or Roller
Aluminum I-Beam or Galvanized
Get disc brakess, bunks, a longer tongue, strap winch instead of a cable, the jack stand that is telescoping, and loading guides it'll make your life 1000x easier.
I also prefer aluminum trailers.
Hope that helps I used to work in sales at the largest boat dealer in my state and have set up many trailers.