Shabbos 22:28

We are not permitted to hang a canopy over a bed on Shabbos because doing so creates a temporary tent. It is permitted to put down a bed, chair or table even though a “tent” (i.e., a covered hollow space) is created beneath them. This is permitted because it is not the way one sets up either a permanent or a temporary tent.

Shabbos 22:29

If a tent has a slanted roof that is not a handbreadth wide (about 3”), nor is the area within three handbreadths of the roof a handbreadth wide, it is considered a temporary tent and one would not be liable for erecting it for the first time on Shabbos. If a cloth is hanging folded over a beam on Friday and cords are hanging from it, it may be unfolded and re-folded on Shabbos. The same is true of a curtain.