Customs COE car haulers questions

Hey I noticed a few of you have some nice COE rigs I was looking to get one and make a hauler out of it. I see from the pictures in the coe thread most people have made there own flatbed. Does anyone have any advice on what to do and what not to with the flatbed? I have not bought the truck yet I'm looking at a few and i have not made up my mind so I'm just picking some brains I guess you can say.

Thanks in Advance
B