It really depends on how you choose to do so. If you have the materials laying around your home already then this would be an easy project that can take as little as a few hours of work depending on however many pieces of wood you need stored away or how large they are. However if you're going with a custom design made from scratch out of new materials such as cedar planks, plywood sheets/blocks using nails/screws during assembly, etc., then obviously things will take longer due to gathering everything together beforehand which could increase the time invested building one by several days compared to just using what you have already. Either way, it's an easy project that can be finished all at once or done piecemeal as time allows over the course of several days depending on your level of commitment and whether you want to make multiple boxes instead.