Windows seem important. I'm not sure if it's for light or if it's supposed to indicate importance of open windows. I plan on having venting and other windows, but I ran across a window my grandpa got ahold of when taking apart a house (which I'm hoping he'll let me use his supplies, that part is... sketchy still). It's about 4' tall and 4' wide. It's split in half because it's a sliding window and I was thinking it would be a perfect way of getting in and cleaning out the pen but it locks so it'd be safe. It's also one of those that doesn't let heat out I believe. But is this too much window? Too much light coming in? Other concerns? Maybe if I painted it... but I'm pretty sure my grandfather won't let me do that. Honestly this is all stuff he hasn't touched in years, it might just be easier to use it and apologize later.