I have followed the instructions listed in the FAQ section. I have placed the Stair down, but cannot go any further. I have also tried pressing the number 2 on my keyboard, and toggling the F10 key but nothing seems to work. I feel as if I'm missing some minor detail on how to build on the second floor, and simply can't figure it out. Any suggestions would be greatly appreciated. Thank you (for the fun game!).

Try Pressing "Tab". Look on the side of the screen for a red and white box. The red box is your "current" floor, the one you are looking at. Hope this helps
-Superjes1