Dan,
Visit the Texas Self-Storage Association website and you can learn a lot in a small amount of time.
Texas Self-Storage AssociationThey've got quite a bit of educational material, and their 'Self-Storage News' magazines have great articles from time to time.
I'm not in self-storage, but many of the articles dealing with planning and building self-storage facilities are applicable for any commercial development.
I do know that prices on existing facilities have been bid up in the last several years, as money is being thrown at industrial and warehouse type properties.
If you build new, know that many municipalities have placed all types of restrictions on the new construction of these facilities. Be prepared to deal with a bunch of red tape.
Good luck.