Building a desk into a bay window is simpler than building a wall-mounted desk, because you have the extra supports of the multiple walls of the window. Bay windows are usually installed to add extra light into a room, and as such are an ideal place for a desk, where you can work with the natural light flowing in. You don't need in-depth woodworking knowledge to create an attractive and functional bay window desk.
Draw a level line around the bay window walls at 75 cm (30 inches) up from the floor. Find the wall studs and mark their position on the level line.
Measure the length of the back wall of the bay window and cut a length of 5 by 5 cm (2 by 2 inch) wood to this length. If the bay window has angled sides, mitre the ends of the wood to fit the wall angle. Position this board under the level line on the back wall and screw in place with two deck screws into each stud. Measure and cut the timber for the remaining walls and attach in the same manner to create the wall cleats, or supports, for the desk.
Measure the length of the bay window opening and cut another piece of 5 by 5 cm (2 by 2 inch) timber to this length. Position this piece of wood in the opening, abutting the ends of the cleats on the side walls. Attach this cleat with two deck screws through the ends into the abutting ends of the sidewall cleats.
Measure the distance between the back wall cleat and the cleat across the opening, and cut two pieces of 5 by 5 cm (2 by 2 inch) wood to this length. Insert these planks, evenly spaced, between the front and back cleats, and secure in place with corner brackets and wood screws.
Measure the dimensions of the bay window recess to get the dimensions of the desktop, and cut out the top from plywood or MDF. Position the desktop on the cleats and attach it to the cleats with wood screws every 12.5 cm (5 inches) around the perimeter of the top.
Fill the screw holes with wood putty and let dry. Sand the desktop, then paint it and the cleats.