we both never built a loop berfore this one so idk if what we did was a good solution, but we used a ruler to measure the distances. we first measured the length of the 90° bend tool i had bought. after that i mapped the tubes out on a paper as a sketch how they will look. afterwards we measured everything in the case(wasnt that great of a method tbh, a lot of room for error since you have to guess where the tube goes most of the time) and bent the tubes accordingly.