scale trailer

[driveshaft]

hi , I am a new member. I have been on here for a couple of months. I just got my first truck, it is a globeliner that is for the most part stock. now I need a trailer, I would like to build one, but need to know what is scale for length? and could someone tell me how to figure out scale my self? I will get some pics. up when I can for all to see what I got. I am going to need some small parts to finish the truck also. but I will get in to that later, for now I would like to have a trailer.