I was going to build a trailer but never got around to doing it.
All new parts from Tractor Supply, they are Carry-On brand.
You'll just need an axle, wheels, and metal to make the frame to your size.
I have the following:
(2x) Fenders
(2x) Leaf Springs
(2x) Weld On Spring Mounting Kit
(2x) U-Bolt Kit
(1x) Spring Tie Plate Kit
(1x) Coupler for 2" Ball
(2x) Stop/Turn/Tail Lights
(1x) 1000lb Gear Winch w/ 40' Cable
(1x) 2000 lb jack w/ swivel plate