Galvanized aluminum ?? I didn't realize they did that. Had to look it up.
If the surface facing the sun has high reflectivity, I would leave it alone.
If it had low reflectivity (dull gray?), maybe some white sealant paint would help.
If you had any kind of shading above the roof, that's going to help cut the heating inside.
I would not use netting that came in contact with the surface, since it might conduct
it's heat gain into the aluminum.
Being a Texan in a former life, I know that aluminum is going to be very hot on sunny days.
Radiant heat is going to cook anything near it, and it's going to warm the air inside the shed.
YouTube - ‪How Radiant Barrier Works - AtticFoil® Reflects Heat Coming Off The Roof‬‏
http://youtu.be/d-ShAiclBt4