There should be plenty of free doghouse plans on the internet if you search for it. The trick to using pallets is to successfully take them apart and then use them as boards to build your doghouse. A hammer and small prybar should be all you need. And maybe a cat's paw or nail puller to get at the really stuck nails/staples. You need to discard the weak lumber and carefully remove all nails, screws, staples that could cut or injure someone. Any chemical stained spots should be discarded also. You may need to go over it with a belt sander to smooth out the fairly rough texture of the pallet lumber and ease any of the sharp edges. Splintering wood should be trimmed. Once you build the house you will probably need to paint or stain it to protect it from the elements. You really can't pick what the pallet wood is actually made from. Good luck.