It was a difficult process.  Holes didn't line up, screws were either too long or too short..bought different screws.  I put two cats out there.  To get them out, the door isn't tall enough for me to get in there to get them out.  I tripped on the board on the bottom.  I almost lost the cat.  WE need to figure out a way to put an opening on the end at top shelf level so it's easier to life and get them out.