I think the other guys nailed it with the cost. I think even having the parts you do it's going to be more expensive than buying a used trailer. Putting full sized 265 truck tires is going to lift the trailer way higher than you want to go, esp if this is being built as a dedicated moto trailer.
I just bought a new Tundra and loaded into the bed last weekend. Crap those are high. My trailer is literally walk up the ramp hell my wife could do it.
If you are going for the "look" of a truck bed, although not sure why that would be desirable personally
, I would buy a trailer axle, link it, and run air bags to drop the bed down to reasonable height. Of course thats a shitload of money and effort to get the desired result that a regular utility trailer has wich will probably pull nicer being lower CG etc.
I would really consider this if this is designed to be truly used and functional because I think the height reality is going to get old quick unless you play for a basketball team.