You can do a skin about whatever you like, aslong as it doesnt break any rules.
The best thing to start would be:
- read the list of important guides thats pinned in this forum
- watch TooFastDans Videos about skinning
- take a look at other skins and try to understand how they achieved their look.
For help you can either use this forum, or I would suggest you to join the skins! discord.