Inspired by The Bristol Polka Dot Dress from Ruche ($52.99):
I used a thrifted long sleeve polka dot tee (no picture) and this thrifted navy skirt:
I dismantled the skirt in order to create the skirt portion of the dress (it had a white lining which I removed and saved for another use). Then I shortened the sleeves of my shirt and cut off the excess length, which I used to make the ruffles on the front. I sewed the 2 pieces together using elastic thread. I wasn't sure if this would work or not but actually, it worked beautifully! (Another great use for elastic thread). It probably wouldn't work if you were using heavier fabrics but because both my top and skirt were lightweight (the skirt is actually quite sheer) it worked well.