Would like to recommend a free service for performing a variety of calculations before construction. You also receive a complete drawing package and even templates for cutting in some of the trickier cases. I've used it myself to calculate a roof, skHipp rafter in English, which I believe is called a valmat tak in Swedish. There are tons of other things you can calculate, everything can be switched to the metric system and printed out. They appreciate it if you donate a little to a charity, but it is not a requirement.
You can find it here:
https://www.blocklayer.com/
