We have a home that is 104 years old. There is a room that was added in the 1940's and built over a sloped roof from the rooms below. It is fully enclosed and we would like to add some shelving in the room. My question is how do we frame the walls that we want to build to attach shelving to. Both the floor and ceiling are sloped. Should we attach the footers and headers to the sloped floor and then cut the studs at angles to make them level or do we shim the footers/headers together or individually? Any thoughts would be appreciated.