I am installing a new Kitchenaid 30" ELECTRIC SINGLE BUILT-IN OVEN under-counter. It is designed to do this and we will be adding a compliant gas cook-top above it. My question is: what material should I build the box for the oven with? I am thinking 3/4" plywood. Any other guidance is always greatly appreciated.
3/4" plywood should be fine for the cabinet. Are you redoing all the cabinetry in your kitchen? I don't think they offer it in Home Depot/Lowes, but most cabinet manufacturers have cabinet units that are designed for wall ovens. Additionally make sure you check the specs on both units so you have proper clearance between the oven and the cook top you are installing above it.