I can't say if this is the proper thing to do, but I can say what I would
Two possible solutions(thoughts):
1. Select the entire model, and use the scale tool to "skew" the model
slightly so that the foundation goes uphill. This may not solve the problem
but it will reduce the amount of sinkage on one end.
2. Remove the roof, break the model into segments, skew each segment
slightly, arrange them upwards like low action steps, build a new roof to
Think of it as building an optical illusion. I would like to see this
myself in GE if you could share the coordinates.