This custom raspberry pi enclosure can fit a raspberry pi 3b/3b+ and an 80mm CPU cooling fan perfectly.The only drawback is that i havnt added opening for the display ribbon cable. But i have attached the step file below if anyone wants to edit and modify.Please note that the design is only for personal use.

Bill Of Materials4 pcs M3 x 3mm (PCB mounting) (SHCS/ALLEN KEY BOLTS)4 pcs M5 x 30mm (Fan Mounting)(SHCS/ALLEN KEY BOLTS)4 pcs M3 x 10mm (Enclosure locking)(SHCS/ALLEN KEY BOLTS)2 pcs M3 x 8 (Din rail bracket mounting)8 pcs M3 x 4 threaded brass insert/ knurling heat insert6 pcs M5 x 4/5/6 threaded brass insert/ knurling heat insert1 pcs 80mm CPU cooling fan

Notes :1) Predrill the 80mm fan mounting holes with a 5mm drillbit for fitting 5mm smoothly.2) Carefully predrill the raspberry pi 3b/3b+ PCB mounting holes with a 3mm drill bits to fit 3mm bolts for PCB mounting.

3D printing settings0.3mm layer height25% grid infillpla