There are some great tutorials out there so u won't b in too much trouble! There are a couple of different ways but the easiest will most likely be to build it out of furniture foam and liquid latex.
Adelheid (KHR!)- 85% done
Fem!Austrian War Succesion France (Hetalia/Nyotalia)- 10% done
Fem!Izaya (Drrr!)- 90% done
Magent!Teto (Vocaloid)- 95% done