Building a ATV rack case?

I have been thinking about the possibility of building my own case for the back rack on my ATV. I was thinking about it last night, if I drew up something that would work as a superstructure, then I can have my brother weld it together from lightweight metal tubing and I just build a canvas slip cover to go over it. I could even add in mesh sides on it and a mesh top with a hasp on it so I can lock it closed if I want to have it be a secure storage place for whatever I want stored in it. Definitely something that I am going to be pondering on.