I want to make a CaS Dress using Sims 4 assets to make a maxis match

[Darkcymru]

I dunno where to start. I want to make one for my personal sim my OC which is deleera, meirith, angela or lilith.

 

I wanted to use one of assets from realm of magic and base game swim suit and combine it into one and change the material of the 

swim suit to leather ish.

 

how can I do this?