I measured the door frame below and wanted to match this size with the transom above. I bought some 1/8th inch window glass and made the frames out of 1x6 boards that I had to rip to 4 1/2 inches. To strengthen the corners I made mortise joints in the horizontal pieces that the sides would fit into. You can see the notches in the picture.
I clamped the frame together on a flat surface with a little glue and held it together with a couple clamps while a put some nails in the corners. The clamps enabled me to square it up perfectly before I nailed it. It needs to be square so that the window will fit right.
Now that the frame was finished I inserted the glass over the muntins I already installed and added the muntins on the other side. This would 'sandwich' the glass in place.
WHERE DID I GET MUNTINS?This took a little improvisation. I ended up buying some pieces of mullion trim that are widely available and 1 1/4" wide. (Mullion is trim that separates different windows, whereas muntins separate panes of glass, at least that's how I understand it...) I ripped about 3/8" off of each edge to use as the muntins. This worked great for this project because the edge profile was a very close match for the muntins used for the doors and sidelight.
It was a beautiful day and this was a fun project. Kind of like craft day at school, except with nail guns...
-Peter