I had to build myself a toenail a few years back when i lost mine in a 'kick the bed base in a temper, barefoot' incident :o
I made mine on forms wrapped around the correct c curve stick to match my toe. shaped and buffed them,
I applied them with adhesive (gelbond I believe is a good adhesive to use for this as it is pharmaceutical grade... please someone correct me if I am wrong, I know things change ? ) and painted them... you couldn't even tell !
I would if it were me, I would probably build on to the skin. I know some people wouldn't agree with this way, but I did it directly onto the skin as mine begun to grow, It was to bumpy to do any other way.
and I have done the same for a 'nail picker' client I have.
The nail/skin isn't a smooth surface, so by building on the skin it will fit in to all the lumps and bumps in that area.
You could try oiling the skin first, then build the nail onto the oiled surface ( mind your brush) and allow time to ease it off again, then make spares, and then remove oil and apply with adhesive.