Have you considered screens on rollers for storing framed works? I think
they are much more versatile, easier to use, more economic per sq ft than
any kind of shelves. Screens are also safer for the art than shelves
because the paintings never touch each other or lean against each other.
We have some adjustable shelving as well -- for unframed works or unusual
objects. A combination of rolling or sliding screens and adjustable
shelves is almost ideal.