Here is a simple way to create a nice looking product while only using PCB's (the PCB manufacturers will love you :) )
Things is that you need PCB's anyway for your electronic product so why not use that as the case also.
Step 1: Component Assembly
For my Solar BMS project I needed 3 PCB's
one for the power components that is a metal core PCB is similar with a normal FR4 PCB but is a single layer and is made out of 2.5mm Aluminium plate (2.5mm is for my particular case can be less) then about 100um (0.1mm) Teflon layer for electrical insulation but with excellent thermal conductivity then there is that 1 layer of coper and of course solder mask and the other things that you want :).
So this metal core PCB (the one with black solder mask) is at the bottom then there are two layers of spacers 1.6mm then there is the main board with all the small non power components I call that the main board then another two layers of spacers that are exactly the same as the ones before and then the last PCB that is the front panel has the cut out of the LCD and capacitive buttons.
But you can get a better picture of how all fits on the next step.
Step 2: Assembled PCB Case
This is how all looks assembled. It makes for a really rigid case.
The thing keeping all together are hex standoffs and one one side flat head countersunk screw so that the back remains flat in order to be installed on a heat-sink. You will need to ask your PCB manufacturer to do this type of holes for you since you can not specify this in a typical gerber file. On the from is not that important what type of screw head you have at least in this particular application.
Step 3: Final Look
And here is the final product attached to a heatsink for increased power dissipation. In this case since the device is high power 40A charging simultaneously with 80A discharging possible the TDP is around 20W and the small metal core PCB can dissipate at most 5W without active cooling or as in this case larger passive cooling.