Sounds to me like the questions are how much you have to spend both to buy and to fix the place and how much you like to DIY. If you figure that the cost of the house plus the expected cost to update are still under the going cost of a similar house in the area, then you have that part of your answer.
While rodding the drain is not a DIY project in most instances due to equipment cost, the roof could be. If all you have to do is reshingle, or maybe sister in some roof rafters, this can be a DIY project. And I'll bet you find others when you live in a 110 year old house. But how else can you get the space and the craftsmanship for the money?