We have one too, insulated the roof and sides, put a floor in, and swapped out those slider doors for barn style wood doors. Added... 4 windows and 2 pop doors. Plus a window in each door. Bedding will collect in the door tracts unless you put a "wall" there to stop it, that drove me crazy!
A sawzall and tin snips is all you need to start cutting holes in it.
A sawzall and tin snips is all you need to start cutting holes in it.