You should talk to moharitgarg. He built his own.
It is mohitgarg.
For the thickness of the case, here it is, top to bottom:
1/8"
3/16"
3/16" <--- mounting plate
3/16"
1/8"
You can find the PCB and case designs on ergodox.org. For the case they have both the 3D model as well ast the acrylic plates design.
If you go for plated, design, you can use any material as long as you feel it is strong enough. For the mounting plate, just make sure that it is solid as there would be many cutouts for the switches and it will take the most beating when you use the keyboard.
Apart from that, switches I have no idea for your location. In India, there are no switches sold, and getting them from abroad didn't make sense, so I harvested a Cherry MX Blue (My Fav) from a TVS Gold (Cheapest MX Blue board in
India the world).
Electronics, order what you can from stores in your region. I got most of the standard stuff, some I ordered through Farnell (They have a Indian subsite, take around 3 weeks to ship but you can get pretty much anything).
PCB I got from the Massdrop groupbuy, because of the overlapping holes, my dealers here were charging me to high a price, otherwise they were cheaper than the MassDrop buy even for a single order.