Well let's start with the case. Oddly yes, I know. However knowing what case your gunning for can drastically change your components.
Going with the Norco 4224
http://www.norcotek.com/item_detail.php?categoryid=1&modelno=RPC-4224

So we have 24x hot swap drive bays, connecting using a SAS backplane with 8087 connectors. Great case, can't really say more than that.
So inside there's the SuperMicro X9DRD-7LN4F
http://www.supermicro.co.uk/products/motherboard/Xeon/C600/X9DRD-7LN4F.cfm

Obviously you can see it's a dual socket. Didn't go with a quad socket as those boards tend to be propriety design and require a certain chassis. This however is a good compromise and with the CPUs going to be paired with it. It certainly won't be lacking on power.
Notable features are:
- Support for 512GB RDIMMs although can use 128GB of UDIMMs
- 4 Intel Gigabit LAN ports. (One would be enough to saturate a 100Mbps line, but oh well)
- Onboard LSI 2308, so capable of 8x SAS2 drives (and 6x SATA)
So now.... the CPUs
Intel Xeon E5-2690 8 cores (16 threads)
These are 2.9GHz clock. Although there are 3.1GHz versions (E5-2687W) unfortunately they suck 150Watts and most non-proprietary boards just aren't capable of powering them. So the 2690s are the next best.
RAM is up to you.
Using non-ECC Ram the board supports 128GB, which is still a freaking alot. So you could use crucial 4GB cheapest dimms. Least they will be cheap to replace if one dies. Using ECC would be better, but its not gunna offer much for use in game servers.
PSU
Both CPUs can draw 130Watts at full tilt and powering the mobo, RAM and any drives is going to be a pull. You also require a PSU with alot of overhead, so that it is running most efficiently as possible.
A Corsair AX860i is going to provide enough power and also has a platinum efficiency. If you wish to run LOTS of HDDs then the 1200watt version would be better.
However this is not very server like and provides no redundancy, however its the best your going to get that can support the hardware.
HDDs and SSDs
So SSD obviously for your OS and game files. 4x Plextor M5 128GB in RAID 5 are gunna blitz around 1.5GB/s in read and write (providing the controller holds up) and also provide an N-1 failover. 128GB fill be fine, as that is 330GB of usable data after formatting and losing 1 drive to parity.
For backup. you can also use a RAID 5 array of 4x WD Reds 1TB. although the capacity is overkill, you dont want to bottleneck in making backups. You could also allow for multiple staggered backups to be stored. Yes you can use just one 1TB drive, but as I said HDDs typically write at around 100MB/s these days.... which is dead slow considering your copying data from an array capable of 15x that.
Although the board has a RAID card built in, you'd still be better off to use a dedicated RAID card, incase something goes tits up with the board and it needs to be replaced.
I've bashed this together quickly and haven't done the pricing (that would take a while, plus im in the UK and i'd have to browse the USA retailers) But to give you a good estimate of pricing. The CPUs are around $1800 each.
PS. I'd go way more overkill on storage if this was more of a general purpose machine.