Hello, I am looking forward to build a computer ( I have never built one!) to mine zcash, and I would love if you could help me. I am learning some stuff, but I can’t seem to find a good combination of motherboard and GPU (and also the number of slots the motherboard should have)! Could you help me? Consider my budget for the computer will be around 1000 euros.
Thank you very much in advance!
You will need around 1200 € for a setup of 4 GPUs
Example
The thing is that I read online that RX 480 is quite expensive compared to the performance (in terms of hashing) is it correct or should I get it anyways?
Get a RX480 8GB if you can. It costs a bit more, but gives you some more headroom for improved miners.
Use MSI Z97 Gaming 5 motherboard. It is BEST deal for mining. 7 PCI-E slots means 7 GPUs possible on one rig!
For video cards, I recommend the Sapphire RX 470 8GB OC (100407NT+8GOCL). They will each mine Zcash @ 155 mh/s with Claymore v7 or Ethereum @ 26 mh/s. Sapphire uses two replaceable fans for better cooling and their cards draw most of their power from the 8-pin connector rather than PCI-E slot… less stress on the risers. 8 GB memory allows for more mining capability (and future optimization) and OCL allows for more settings modification to get more efficient mining. You will have more fun!
For risers it is vital to remove the molex/sata adapter and ONLY ATTACH THE PSU → 4 PIN MOLEX CONNECTOR DIRECTLY TO THE RISER. The SATA connector cannot handle the amount of juice and will burn. Promise you!
Risers, look for ver 005 or ver 006: http://www.ebay.com/itm/5X-60CM-USB3-0-Power-Cable-PCI-E-Express-1x-To-16x-Extender-Riser-Card-Adapter-/291908203369?hash=item43f715b369:g:vaoAAOSw4GVYKs0d
Use this power supply with modular connections: EVGA 1000GQ 210-GQ-1000-V1 GQ 80 Plus Gold, 1000W ECO Mode Semi Modular Power Supply - Newegg.com
Order extra Molex cables from here: http://www.ebay.com/itm/New-6-PIN-PERIF-to-3-x-Molex-flat-4-Fan-etc-Power-Cables-for-EVGA-Modular-PSUs-/162273213763?hash=item25c83cbd43:g:nRIAAOSwzaJX-Tzr
Just get a 470 4gb, pretty much same speed as the 8gb but much cheaper.
Avoid 480 all together with mining.
Wow, Rafikichi, you were very kind with this answer actually, and very complete! I really appreciate it! but getting that motherboard, I would need to get 7 GPUS, and if I get a RX 480 it is going to cost so much. I am a very small fish, thus I was thinking of 1000-1200 euros budget, and thank you so much for the advices! I am really looking forward to build this computer and can’t wait to have fun with it! 
Avoid it because it is too expensive compared to the hashing power it gives back?
so what GPU would you prefer ?
I just use Asrock H81 pro BTC v2, cheap celeron G1840, 4gb ram, any 120gb SSD. $90 mobo, $45 cpu, $25 ram, $40 SSD. For PSU, get any gold psu with 6 pcie connectors. Don’t cheap out on the psu, buy a good brand like EVGA.
850W psu is sufficient for 6 undervolted cards. But 1000W - 1200W is better in case future coins need more power.
Then 6x Rx 480 8gb, or Rx 470 4gb. Rx 470 for faster ROI, Rx480 for future proof, who knows future miners or coins are better with 8gb cards. I buy half of each card to be safe. Get the cheapest card, single fan or reference doesn’t matter. It’s not like we are mining litecoin and need the cooling.
If you’re adventurous, you can try 7 gpus on Msi Z97 gaming 5. Cryptomined on youtube had a video on this 7 gpu mobo.
I’m sticking with this H81 btc though. If it’s not broken, don’t change it 
Yes,
its only a little faster but much more expensive.
Really interesting advices guys! Thank you so much! I will now look into it, and see what the best combination for me could be. Last thing, should I care about processor? or only about graphic cards for mining?