Pella Skylight - Sash Groove

I recently installed a Pella fixed skylight and I am about to put up the drywall for the ceiling. I am curious about how I should finish the work between the skylight sash and the ceiling drywall. Do I use drywall or wood? The skylight sash is about 1-1/4" thick with a groove around the perimeter facing into the room that is about 1/2" wide. Is this a standard groove configuration? If so, will I find mating lumber at the home improvement stores, or do I need to do some fancy router work?
TIA for any replies, JP
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.