how steep can the ramp up to the coop be?

[oak_abode]

Not safe for feet:
https://www.backyardchickens.com/threads/ramp-too-steep.545752/page-2#post-20341706
It's not saving space either, putting low end of ramp up on a 16 high concrete block would actually make more space under ramp available.

Yup! Already updated to the wood treads, working great!