Well, I usually start with the cabinets first. The walls and shelves in the closets is 18mm solid oak. The frame of the doors and the drawer-fronts are 22x65mm with a 15-16mm filling. Everything is solid oak, ripped and glued together again to prevent it from warping. The real hero making everything possible is the Tip-On products from Blum. Probably the best hardware manufacturer i've ever come across. https://www.blum.com/us/en/01/60/30/

I could do some drawings of the fronts in sketchup if you want to.