[header] How to build a window box [title] Find inspiration. [step] Look at varieties of window boxes online or prefabricated models in stores to get an idea of the design you would like to use. ( the instructions that follow are for a basic rectangular box. 
They can be easily modified to fit whatever specifications you are looking for. ) [substeps] In particular, you may want to think immediately about how your window box will be attached to your house.