Boneh (Building) - Breaking Down the 39 Melachot

It's Friday night, and you realize you forgot to  set up a pack and play for your guests. Are you   allowed to build a pack and play on Shabbat?  If you're walking down the hall and you see   that a mezuzah fell down, are you allowed to  reattach the mezuzah to the doorway? And lastly,   if your children want to build a tent out  of the dining room chairs and a blanket,   are they allowed to do that on Shabbat? One of the  Melachot of Shabbat is the Melacha of Boneh, which   means building. When it comes to reattaching  the mezuzah, you are not allowed to reattach   the mezuzah to the doorway on Shabbat. Instead,  you should make sure to pick up the mezuzah and   put it in a respectful place. Your children  are not allowed to make a tent by draping a   blanket over chairs on Shabbat. And lastly, you  are allowed to build a pack and play on Shabbat   because the entire thing is already connected,  and it's simply standing it up in a specific form.