"could i use mostly wood to keep the heat inside the enclosure and screen off a smaller portion of the top?"
Yeah, you can. The wood would need to be sealed (polyurethane or similar coating) in order to keep it from warping, getting damaged, from humidity.
"what would be the best way to heat the enclosure, heat pads/mat & lights?"
That's gonna depend on what you decide to put in there (type/species of animal). The top should be made after you decide what species you're gonna get, that way the top can be designed to work with the methods of heat & light. They'll go hand-in-hand.
Once you decide your critter type you can go to that specific forum and ask for advice from those with experience with those critters.
Here's a pic of a top I threw together in a hurry to get me out of a jam. I didn't have a top for a 55-gal. tank that I needed to temporarily house a Burm in so I made one out of wood, plexiglass & screen. The screen is under the dome light and the plexiglass has several small holes drilled in the opposite end for thermal regulation.


Take care!
HH
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It is said that 1 out of every 4 people are mentally unbalanced. Think of your 3 closest friends, if they're normal, then it's you.