You will want your dog to be able to be comfortable in its new home. Therefore, you will need to design the house so that Fido can sit up or lay down and stretch out. Add about four inches to these measurements and then you are ready to proceed. The next step is to figure out how much lumber you will need. For the frame of the doghouse, two by fours will work fine.
Treated wood is an excellent choice as least as far as the frame pieces are concerned.
Thick plywood is a suitable choice for the floor, roof and side walls. It can be measured, cut and then applied in one piece, and it is easy to work with. Of course, you will need to shingle the roof for protection from the elements such as rain and melting snow. You may choose to paint, stain, or even put house siding on your finished project, the choice is yours. You can build your doghouse in many different designs, but there is a basic design that works quite well for even the amateur carpenter.