There's been times when I've temporarily "stored" stuff on my ladder.

A glorified or altered ladder? Might only be useful for small items.

How about alternating shelves, somehow, like alternating stair steps, as a design option?
http://www.bing.com/images/search?q=...BF4CAF&first=1

http://www.bing.com/images/search?q=...26698&first=83

Wall mounted cat ladder approach? Don't know if this is applicable, but this may lead to other ideas from someone else: http://www.bing.com/images/search?q=... nt+cat+ladder

Sonny