Hi Rama1065,
If you consider the "building block" concept idea then please have a look at a picture I made a while ago and I shared before:
How big each "building block" would/could be, I leave that up to you, for example each at 84 HP. In such example if you would have a monster case then one row of 168 HP could consist of two building blocks. Naturally a few blocks can be merged together to save space too.
Hopefully this will help and kind regards, Garfield.
Edit: I forgot to mention this below link here in the forum, it's discussing this similar topic, perhaps interesting for you?
https://www.modulargrid.net/e/forum/posts/index/9489
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads