That would probably depend upon the price of wood and tin in your area.

Most of the people in FL put a roofover on their mobiles and this consists of actually building a roof higher than the mobile and closing it in in the front and sides. They also cover a rear patio and leave the attic area open for storage and such.

Figure on trusses every 2 or 4 foot. You will want an overhang by at least six inches on all sides.

And the height of the roof peak is up to you but that extra space allows for cooling and air flow.

What you save in heating and air conditioning bills will pretty much pay for the roof.

Most people that are DIY'ers find it easier just to do a tin roof.

Trusses are normally formed by angled cuts of 2 x 4 with a triangular piece of plywood nailed at the peak for stability.

Draw out the plans and measure them and then count how many 2x4's you are going to need to accomplish that.

Thank you brezynosacek.
Dan