Standard, yes.
So far i've only sculpted add-ons, or a covering for an arm or body with new armour or clothing. I haven't tried doing something completely new, i always have a plastic 'skeleton' to work from.
I often cut down a plastic body and cover it in a breastplate, or chain mail hauberk. I might try that some time, but for the moment i have plenty of spare parts to use as a base!
I've done a couple of tries making my own figures, but i'm never happy with proportions, hence the reason i only convert existing figures. Maybe one day ??
There are some examples of stuff i do on my blog, and i will be sharing some more things here soon.