Making things square

In my previous post I mentioned the importance of making things square. This just means that making angles 90 degrees I had to do this for the lower half of my dog house more then the top, because I made my rooo at a slant. The easiest way to make sure your angles are correct would be to use a square, which is a tool that is shapped like an L and is 90 degrees on every angle. Althouht I feel like my square was a it warped from the cold temparatues and thus wasn't 90 degrees like I though. Once you start you must follow through with the plan. My plan was to just stick a sheet of plywood on top to make my roof. But my mentor said I should insulate the roof,which I did, but my plywood on the side did not meet the roof due to the change in my plans. Which resulted in theri being cracks in between the roof and the walls. So always follow your plan.