If it's only going to be used as a mining rig, I would skip the case and build my own BBT open air mining frame below for about $40 out of two 8ft pieces of 1/8" x 3/4" angled aluminum, one 8 ft 1" x 3" piece of pine, one 4ft 1" x 2" piece of pine and #8 1/2" self-tapping screws or out of all wood if you want to save some money. The cards will run cooler and it will easier to add more cards later if you want to.
For a motherboard I would also go with a dedicated motherboard like the Biostar TB85 for the same reason. You can put one card in the 16X PCI-E slot and use a USB riser for the other card.
https://www.newegg.com/Product/Product.aspx?Item=N82E168131384366 GPU Frame (Dimension 21" W x 15 3/4"" D x 10 3/4" H):
Build Cuts:
For the Angled Aluminum:
-First 8ft (96") Angled Aluminum; .75 inch of waste
4x 15 3/4" cuts (63" use) (Case Depth)
3x 10 3/4" cuts (32.25" use) (Case Height)
-Second 8ft (96") Angled Aluminum; 1.25 inch of waste
4x 21" cuts (84" use) (Case Width)
1x 10 3/4" (10 3/4" use) (Case Height)
And for the wood:
-8ft 1x3 Pine (96"); 2 inch of waste:
6 cuts of 15 3/4" (94" use) (Case Bottom)
-4 ft 1x2 Pine (24" left over):
1 cut of 21" (21" use) (Card Bracket Support)
https://www.youtube.com/watch?v=D5xNrlxsCVshttps://www.youtube.com/watch?v=MA_sH4q2toU&feature=youtu.be&t=283