The backdrop I am about to show was something I saw multiple times on Pinterest. I didn't follow just one person's advice so I'm not giving credit but also not claiming this idea as my own.
My son, the Princess's daddy, bought the table skirting and a package of balloons at Party City. The balloons are attached to cardboard tubes used for pouring cement footings. I can't say more about that, I wasn't part of the process and didn't see the construction, only the end result. The spires are simply paper. Those posts are attached to the rafters to keep them in place from falling down as small guests run around.
The tablecloths are from a dollar store. Each one was 54" wide by 9 feet long.
I layered three together and held them in place using hair clips that I keep on hand for the Princess.
To make a casing for the curtain rod, I used staples. The depth of the stapler determined the size of the casing.
Having a cranky knee that doesn't like me kneeling on the floor, I laid this stapled trio of colors on my table and cut strips of all three layers from the bottom edge to 12 inches below the casing. I did have to keep moving this since my table is nowhere near that long, but the clips helped keep things together and it didn't have to be perfect and evenly cut. Each set of streamers was braided with two repeats and then stapled to hold the braid in place.
I had intended that the pink layer would be the "right" side but that isn't how I turned the casing. It would have been okay this way, but purple side does look neater. These views are in my home, showing one set of three cloths used, roughly 54" wide.
Here is my favorite Princess waiting for her subjects...oops! I mean guests....to arrive.
It was a royally wonderful day.