I would like to remove the old walls and floor to put in a foundation and then redo the walls with 2x6 studs and the floor with 2x10 joist . The foundation is just three brick deep and sitting on the ground. It needs to be 3' in the ground for frost line . And the walls are sawmill studs real 2x4 and no headers over windows or doors and not on 16. And no bottom plate or double top plate. So if it is possible to leave the roof and just replace everything else please tell me. I am planing to just do half of the house at a time. ( How do I brace the roof to do the work.) Thank You

This isn't an easy or safe project for someone who doesn't have the proper equipment or experience.

A house mover can raise the house for the foundation problem,allowing you to excavate the entire foundation ,lower the house and begin piecemeal removal and replacement of the walls and floors, again,this is not for the novice.

Get a professional or 3 to look this over and give you not only their bids,but their thoughts as to how they would approach this.