Made a tutorial if anyone needs help on getting started: How to make a Starter Character w/ Mesh Deformities on Roblox
@RFL890 Literally so cool! Did you uv the mesh to make it fit Roblox’s clothing template?
@skywildsaturn What Yuuwa said! 
If you have the rig, weight/skin paint the skirt to the rig and import it like you would usually do to studio. Then delete the rig and place the skirt under the real rig you want the skirt to go onto and weld the skirt and Root (parent of the joints) together. The weld should be under the skirt and not the Root.