Trailer build questions

[Jamithan04]

Hey all, I don't mean to be a bother to anyone but I am very new to scratch building. I have just gotten a grand hauler and about 1/3 way done building it and I'm in need of a trailer. Wanting to start with something fairly simple so was thinking a flatbed. But I am at a loss on where to start, what should I get first, how do I figure the measurements for the mounting hardware for axels and suspension, what pieces should I get first. I am also somewhat of an ocd perfectionist. And I feel like I need to have everything at once so that mean I need to buy everything, well funds do not permit that. So I am reaching out to all seasoned builders, both kit and scratch and was hoping you guys could help me with this build. I appreciate everyone's time thanks