Can Assets Objects custom fields be created with the API

Hi there,
I find with a lot of my customers I am creating the same custom fields over and over, especially around assets. I have some powershell scripts that I use to create schema, then object types and attributes, saves heaps of time.
I am hoping to be able to create a script to build out the Assets custom fields also, didn’t see anything about it in the API doco?
Does anyone have a solution around this or ideas about how to do what I am after (if possible) or it will just be a manual task?

cheers