Chair rail molding
Baseboard moulding to match bedroom
Drill and driver
1. Mark a level line beneath the windows at the desired height of the window seat (consider if you will be adding padding)
2. Use a studfinder to mark studs of exterior wall. Mark another level line Ύ below the first one to allow for the height of the MDF
3. Cut 2x4 in three pieces to match width of each window. Screw into studs in wall along second (lower) level line. The bench seat will rest on these pieces.
4. Cut two pieces of 2x4 to length of entire bay opening. These will go horizontally along the floor and above to support the seat. Cut enough pieces of 2x4 to go vertically in between in 18 centers. Cut these shorter pieces to the desired height of the window seat, minus the long 2x4 top and bottom. Form a rectangle with the two long pieces on the outside, and to short pieces on the inside, driving two screws through long pieces in short ones on either side. Evenly space other short pieces between, forming a sort of ladder. Screw in place.
5. Set this ladder in front of the bay window. If un-level, add shims. Screw in place into floor and bay window walls.
6. Cut MDF sheet to fit on new wall. Screw into place. Create a paper template of bay window shape to make bench seat, adding a 1 overhand at the front.
7. Cut chair rail to go along front of seat top. Nail chair rail in place with finishing nails. Set window seat in place, leaving unattached for storage access.
8. Prime and paint in desired colors. Add baseboard along front.