Type theory textbook/resource for someone interested in working on type theory

Question

I can think of two motivations for studying type theory:

1. Understanding and applying existing type theories. E.g. taking the calculus of constructions and using it for theorem proving.

2. Working on new type theories.

I have so far mainly been motivated by nr 1. Is there a good textbook/other resource that one would recommend for someone motivated to do nr 2?