Please see this post about a Bodice Sloper is and a video that I used to make mine for Arisu.
Some of the measurement changes I need to make is the neck line, the shoulder length needs to be half, the location of the arm pit (the cut out and measurements were off, so halfway between would probably work better), and the bust line needs to be decreased. That should make a good sloper. When making real clothes though it is not going to be skin tight like a sloper is. The current bodice pattern is going to be modified to make a sweat shirt since it is close to the look I want.
Keeping in mind when making clothes for your BJDs that the thickness of fabric can change your seam allowance. Plus, you have to make sure you can get the clothes on and off your doll. Whether you put it on with limbs off or if the doll has enough flexibility to allow clothes to be put on.