So I followed Julia's directions for a majority of this dress.
However, I was using 2 Medium adult tees [Which worked out pretty well]
I was also using inches rather than cm, so instead of 3 cm gussets, it was about an inch, and then about 6 inches on the bottom [So it's a pretty loose fit]
I used both black sleeves on the front of the top, making each one about 10 inches long and having them meet in the middle. The back of the top is one of the red sleeves I had left over.
The straps are the hem of the black shirt.
This was pretty fun despite a few confusing parts in the middle.
I'd reccomend this to anyone with some spare clothes for upcycling.
[Sorry about the picture. I didn't have a neutral background, and the dress is kinda wrinkly. . . Especially the back. . .]