Show us your design and we can probably help you with what size of plate steel needs to go where, and what location of bracing you will need.
If you are planning to mount a winch, that portion will need to be 1/4" plate. A lot of people will build the rest out of 3/16" to save on weight, but it is still plenty strong.
I am building one for my TJ along a simple design that uses all 1/4" plate. I will add some bracing under the top portion to add support for a winch. Even with 1/4" plate, it is a good idea.