Another critical look out is the electrical. Not only should ALL of the wiring be inspected for integrity (rodents can reek havoc on old wires and new ones), but electrical boxes from the 1920s – or even the 1970s – are not designed to handle modern electrical demands. Blowing a fuse every time you vacuum a rug with a lamp on or the heater running sucks.
Another thing to look out for are the trees around the house. Large, beautiful, old trees are a delight to look at and their shade is valuable in the summer, but dead branches or invasive roots can cost a small fortune when storm comes along and leaves a hole in your roof or blows a hole in the floor from a lightening strike.