For an inset you can use 2x4's on flat against the bay, then place 3/4 ply (oak-maple-birch your choice) across the top.
If you are a beginner use a template for the top. The edges can be covered either in a glue on banding or you can rip a 1/4 off of the matching 1x stock.
For the drawers I would use 2 sets of full extention glides, that makes the drawers 1 inch smaller that the openings.. you'll probably get two 20" openings.
Place 3 gables (uprights) for the sides of the drawer (one center) you can bring in the 2x4 to help support them or screw then in I'd also put a 3 1/2 inch kick, or match the surrounding base.
I made this short but it should get you the idea... putting on the face & those types of things I didn't put in. If you want to see one of the ones I did, ask and I'll place a few pics on my forum for you.
Alter Eagle Construction & Design