Welcome to the boards!
There really isn't a formula that will get you where you want to go. Do a search for DIY sump/fuge and there is plenty of info on these boards. Then when you decide what you want for the tank and what you want to keep. Just ask questions.
It really comes down to what you have, what you want as livestock, tank size and how much you're willing to DIY or buy!
Welcome
HTH
Tim