Depends what kind of finish you want. Home depot sells 4'X8' sheets of oak faced plywood. Then just put 2/3 coates of Helmsman varnish on it to seal. Have my top for 3 years still looks brand new
depending on size of system...you can use all kinds of wood....goto lowes and home depot to get some ideas...and prices...
for me i have a 30g cube...and i wanted wood thats light and solid..its 1/2"....i found craft wood to be a great candidate....its very light and its solid wood....not plywood....i bought some at HD...i believe craft stores will have it too....
but yo just gotta plan out how you want the hood...and then go look around for something that will work....HD also has pine which will make a nice hood also...
this will really depend on your woodwork skills....
as for the wood finish...i used minwax wood stain and polyurethane clearcoat..
Iam I safe to assume that you are going to paint it Black?
I prefer to use hardwood when I build stuff as opposed to soft pine.
Poplar and birch plywood would do well easy to sand prime and paint
be sure to use stainless steel fasteners