All I needed to buy was two leather (or in our case faux leather, as I couldn't find any real leather and didn't want to wait for an online order to arrive) straps. In case you don't already have an IKEA Grundtal toilet paper roll holder you will also need that and the screws and dowels to secure it in the wall. The Grundtal holder currently costs 6.99€ in German IKEA stores. As for tools you need everything to secure the toilet paper roll holder in the wall plus a punch hole and a carpet knife.
Here's how you go about:
1. Get everything set up so that the toilet roll holder could be screwed into the wall.
2. Take the leather (or faux leather) straps and cut of the ends with the carpet knife. Make sure both leather straps are the same length.
3. At the ends of each straps punch a hole at approximately the same position. It shouldn't be too far in, but also still have enough fabric of strap to support some weight. (I'm not sure if this will work with a regular hole punch if you're using real leather but it worked for the faux leather.)
4. Now take the straps and the toilet roll holder and secure them on the wall: You take one screw, push it through the hole of the toilet roll holder, and then place one strap folded over the screw. You will have a loop hanging down now. Also do it with the other side and then secure it in the wall. It looks better if the toilet roll holder blocks the view of the ends of the straps but you could also place the straps on the screw first if you'd prefer that.
5. Tuck in a nice magazine, your current read, or whatever you like.
It's a super simple and quick DIY / IKEA hack. Trying to find the leather straps took way more time than the actually making of this. After checking at a couple of stores I decided to go with a faux leather strap that is actually used for making purses. It's from Rico Design and cost 8.99€. They are black and made of artificial leather and 60cm long each. So far even after a few months it still looks good and withstands the humidity in the bathroom.
Please let me know how you like this DIY and don't hesitate to ask if you have any questions.
Enjoy your now updated bathroom,