Turning Ground Tent into RTT

So I am new here and I am currently building an expedition trailer. I have looked up some stuff for storage and sleeping (RTT), I would like a 4+ person tent but from what I have seen they run for about 1500+. So my solution to this is to turn my 4 person ground tent into a roof top tent, I I just started this idea/design today. If you have any suggestions on how to construct the base plate that the tent will sit on or on any other design feel free to comment. Keep in mind that I am a college student and I don't have a lot of money to spend, hence why I am going this route. Pictures are welcome.

 

https://www.tacomaworld.com/threads/cheap-rtt-for-those-on-a-budget.478273/

Check this out

 

build your trailer with the roof the size of the tent floor maybe and bit bigger. Build in tie down points so you have a place to replicate where you would stake the tent down and just set the tent you have up on the roof of the trailer. set up and take the tent down like normal.

 

Pretty sure most 4 man tents will be too big for that, which is why most RTTs fold in half. If it was wide enough, it would be excessively wider than normal track width.

This is probably out of your budget, but my friends just released their new DIY trailer kit:
https://www.trailtestedmfg.com/