First question is how big of a truck. I'll guess that you would be looking at a "one ton"-which is typically a Ford F-350, Chevy 3500, GMC 3500 etc-bottom line a truck that has a factory tag of 10,000 lbs. You should be able to find numerous clean one tons- equipped with steel dump bodies or raack bodies that have hydraulic hoists. And today, most late model trucks in this wt. range are equipped with electric hydraulic hoists-much like the electric hydraulic hoist used on a snow.plow.
I'll also assume that yo do not have a CDL drivers license which means if you go bigger than a one ton, you will be looking at something no bigger that 26,000 lbs gvw. These would be trucks like a Ford 650, F-600, Chevy C-65, International 4300. these trucks would typically have a PTO opening on their transmissions that would drive a hydraulic pump for the dump body.
So first step how big a truck. Second thought, I would not mess around with some guy who thinks he can build a body. What you are looking for is too readily available-be it a steel dump or a rack dump.
My two cents