So, Shortcake, the top of a queen size mattress is usually 60 x 80. You need to decide how far you want the sides to drop (like a bedspread). When I add borders, I measure the length (93) and cut the width I need for each side. With 4 yards of fabric, you have enough to cut that length without having to piece it. Does that make sense? 4 yards is 144" in length.
Say you want the width to be 100", take 100 - 64 = 36 ÷ 2 = 18". Add 1/2" to each piece for seam allowances. So, you cut two pieces: 18 1/2" x 93". (Just remember that amount, 37", leaves only about 7" from the width of fabric.)
After you've made those calculations, then you can measure what you need for the top and bottom, or just the bottom, if that's the way you want it to look.
Measurements depend on the height of the bed you want to put it on.
I hope this has helped. Wish I could draw a picture for you!