I have been thinking of building something similar for my grills.
There is a thread with several pages of designs and builds.
You are only limited by your budget.
A simple design would be 3 4 by 4 centered posts,6'OC, with 3@4' "T" top and 6@ 3' "Y" kickers.
I would slope about 2/12, drain to the back. You could use 3@12' 2 by 4 for per lings.
You don't need shelves. Just pick yourself up an old gasser.
Hope this helps,