Here is what i have selected for my mining rigs:

Motherboard : ASRock H97 Anniversary

Many miners use ASRock H81 Pro BTC which i have also selected it in the first run but then i decided to go with ASRock H97 Annyversary (specs) because of new chipsets and it can be sold easily after i am done with mining (if ever comes to that).
The Asrock H97 Anniversary (ASRock ATX DDR3 1066 LGA 1150 Motherboard H97 ANNIVERSARY) comes equipped with PCIe 3.0 x16 slots, but the Asrock H81 Pro BTC comes with PCIe 2.0 x16 slots. Even though, currently, the performance difference is negligible, the H81 Pro BTC may not be able to keep up with advancements in GPU technology in the further future.

AMD Radeon RX 480

AMD Radeon RX 470

IMPORTANT: If you are going to have a rig of 6x cards with one of this two, then you will have to get a much powerful PSU and which i recommend this one Corsair RM1000 80+ Gold Certificate 1000w

CPU/Processor: Intel Pentium Dual-Core G3258 3.2GHz
Intel G3258 4 Pentium 3.20 GHz 3M Cache 2 Core Processor
Compatible with Intel 8 or 9 series Chipsets
LGA 1150
2 cores
3.2Ghz base frequency

RAM/Memory: 1x HyperX Fury Black 8GB DDR3 1600 MHz
Kingston HyperX FURY 8GB 1600MHz DDR3 CL10 DIMM – Black
Asymmetric heat spreader for stylish heat dissipation
Compatible with Intel and AMD platforms
Easy to install – Plug-and-Play functionality
SSD

PSU/Power Supply: EVGA SuperNOVA 1600W G2

Corsair RMx Series, RM1000x, 1000W, Fully Modular Power Supply, 80+ Gold Certified, 10 year warranty
The latest ATX12V v2.31 and EPS 2.92 standards and it is backward compatible with ATX12V 2.2 and ATX12V 2.01 systems.
4th generation Intel Core processor Ready (Intel Haswell and Z87 motherboards)
80PLUS Gold certified, delivering over 92% energy efficiency at real world load conditions.

Other parts:

USB 3.0 cable extender with PCI-E Riser
Ill suggest you to buy more than 6 because some of them can have some connection problem or something related. My advice is to buy at least 10 so you can have a few as backup, buy 15 if you can!
Fixable PCI-E 16X to 1X Adapter USB3.0 USB 3.0 Riser Cable Flex Flexible Extension Cable w/ Molex 4 Pin Power

Connector
Can be used in 1X, 4X, 8X, and 16X slots on your motherboard
Fixable board with 4 holes available on PCI-E 16X side to fix PCI-E 16X connector on motherboard for more convenient management for graphics card.
Power and reset switch cables for the motherboard

Desktop Computer Case Power Supply Reset HDD Button Switch

Cable Length : 1.7m / 67″
Material (External) : Plastic, Metal
Weight : 110g
Package Content : 1 Setx Desktop Power Button Switch
Keyboard

AmazonBasics Wired Keyboard

Low-profile Keys Provide a Quiet, Comfortable Typing Experience
Simple Wired USB Connection; Works with Windows 2000, Xp, Vista and 7

Thermal Compound ARCTIC MX-4 Carbon-Based Thermal Compound, Non-Electricity Conductive, Non-Capacitive, Non-Bleeding – 20g

Non-Capacitive, Non-Electricity-Conductive, Carbon Micro-Particle Based Thermal Compound
Non-Curing, Non-Corrosive, Non-Bleeding, Excellent for CPU/GPU/Electronics/Lighting Cooling
Low Thermal Resistance/High Thermal Conductivity Dissipating Heat Efficiently
Ethernet Cable: Tera Grand – CAT7 10 Gigabit Ethernet Ultra Flat Patch Cable for Modem Router LAN Network – Built with Gold Plated & Shielded RJ45 Connectors and Generation 3 Mold, 25 Feet White

ULTRA FLAT – CAT-7 10 Gigabit Ultra Flat Ethernet cable, slim and flexible, easy to fit into the tightest spaces
10 GBPS DATA SPEED – Compliant with ANSI/TIA/EIA 568-B, 2-1, Up to 10 Gbps Speed and Meets all Proposed CAT-7 Requirements; Supports: 10GBASE-T; 1000 BASE-T; 100 BASE-T;
10 BASE-T
PROTECTION FROM INTERFERENCE – Shielded Twisted Pair and RJ45 Connectors to Protect Against EMI/RFI Interference
Watt usage monitor like “Kill a Watt: International P4460 Kill A Watt EZ Electricity Usage Monitor

Calculates cost and forecasts by week, month, and year
Displays eight critical units of measure on the large LCD display
Built-in backup of accumulated information.

Case:
Aluminium frame

Happy mining