Hello! My husband and I are going to build 4 of the large wood dog kennels from this site. We will need to modify the plans for 2 that are larger than this and 2 that are smaller and I think that I have that figured out. however, the 2 smaller ones will double as a window bench seat and I am just trying to make sure they are sturdy enough to do that. anyone have an idea how i can determine how much weight they can handle on the top?