Renovate cottage

Have you ever noticed that often when it is shown how to do different things, it's the simple parts shown. For example, I've looked around for how to add a roof, and what I think is klurigast is how it begins and ends.
How to quit with roofing felt so that it will be tight? Do you let the roofing felt to be in the last board, or lets you tjärpappen be up to the barge board. I tip on adding tjärpappen around the last board and nailing it in, but have not seen somewhere on the way to do it.
Another thing is how you make sure it is tight, but without the risk of fire where the chimney goes up through the roof.
There are certainly lots of other examples. Write and tell us about your own and share with you links where you can find answers.