My first darkroom was in my bedroom. I got some thick black plastic sheets, cut them to the size of my windows and attached them with velcro. Worked perfectly most of the time. In high summer I found the heat from the sun could melt the glue on the velcro and the blackout would fall down. I used to fold up the plastic sheets when not in use and after a few years they developed pinholes at the folds. I also once left some chemistry in an open tray and went to bed - I had a rotten headache the next day.