Europe/ 90km street legal electric bicycle

I would like to build street bike, triangle rear, possibly rear shock, rear hub electric bicycle. Havent seen any good open source designs yet. How does one go about building this type of bike. Surely there are some designs out there with funnily small battery, but I want to be able to fit my own battery and motor controller. Also I am aware of australian type DIY frame, but its to offroad for my purpose of pedaling on well paved roads.

This mopeds used to be made here in Slovenia,.. maybe mid drives ARE the future, and its just about converting this design to electrix. I dunno, so confused

And now this design can be made so much better, with torque sensing, crusie controling adapters and whatnot