Here are the steps to build a window seat:

1. Make cuts for the window seat box.
2. Build the center box.
3. Build the frame for the center box.
4. Add lid to center box.
5. Build corner boxes.
6. Build a frame and lid for corners.
7. Sand window boxes.
8. Install window seat boxes.

For more detailed instructions, you can check out this tutorial from Better Homes & Gardens . Another tutorial that you might find helpful is from A House We Built . Sensible Digs also has an easy-to-follow tutorial . Checkatrade has a tutorial that includes cabinets . This Old House also has a tutorial .