@Ana1234 - It depends on the house. One thing I will say is that anyone who doesn't have much experience with this shouldn't even buy a house with structural damage. The first thing you want to do when looking at a house is to get an inspector to give you a run-down on how solid it is. Cosmetic problems are nothing to fix compared with having to replace a roof or plumbing or foundations.
If the home is of historical value, it might be worth saving, but in that case you've got to be able to restore it rather than just fix it. Another thing to take into account is that older homes are often built without modern conveniences in mind, and might not have efficient energy systems in place.
Buying a fixer upper can be a wonderful decision and, in theory, you are doing something good with your time and money, but only if you pick the right kind of house in the first place.