I’ve been working on this Large corexy design. Its not done but close enough that i feel its good enough to share now.
Here is CastleXY my large printer 
So far the Z axis is the main pain in my side, some ideas would be welcomed.
Here’s a Step file to have a look at if you’d like. https://drive.google.com/file/d/0B0vhoxse_2m0blI3VzAweVdwZHM/view?usp=sharing
If you’re going belted, 1 motor to power both screws should be enough linked by a belt, it’d stop the screws becoming unbalanced due to independent motors. I’d run a couple of linear rods up the opposite sides to the lead/ball screws stop it tilting, not that it will but having them there won’t exactly hurt and will make double sure that it doesn’t bind.The only worry for me would be guiding the bed so it doesn’t bind with the dual screws, if the tension on the wheels gets a little outta whack. Also using 3 wheels instead of 4, with the single wheel side on an eccentric nut will allow for easy tension adjustment of the Z stage.
Also, if using a guide rod for Z - use one, centered opposite from the Z drives.
Planes like to have three point of definition.
Potato chip shapes come from 4. 
You might have to worry about the straightness of the aluminum extrusions in a Z-design like that, I.e. There might be a spot where you lose preload (probably the center) and a spot where it might bind (edges maybe)
Depending on costs, it would be kinda nice to have some 16mm+ diameter chrome-plated shafts as your Z-guides and LMFxUU bearings mounted on your bed. If that’s too expensive, check out the OpenBuilds vslot/c-beam profiles and work those into your design; just make sure you have wheels/bearings riding on both sides of your extrusion to give you consistent preload
@Ishaan_Gov I’ve spoken to Jordan about this before, those uprights are 4040 extrusion…
@Ax_Smith-Laffin I should have mentioned that there is a limit to closed loop belt lengths unless i have been missing them…
I have looked into smooth rods aslo i have 20mm flanged bearings in that case. But there’s another issue with all this added rods and supports is getting the parts out of the printer… The build area is going to be used to the max and not being able to get the print out is kinda an issue.
@Ishaan_Gov The legs on the printer are 1.5"x1.5" extrusion. the build plate supports are 2040
The open rail wont fit my 1.5" extrusion at all. Id like to avoid having to get 15mm linear rail for this.
I built a corexy printer with a 16x16 inch heated bed. I used one nema 23 stepper driving a open builds linear z axis centered on the back of the bed, plus a GT 2 belt from that drive’s 8 mm thread rod going to 2 more 8 mm thread rods on opposite corners of the bed. I’ve previously posted pictures and videos of it.
Hi is a photo of my Castle CoreXY
missing/deleted image from Google+
You got me there! haha.
I change the name 
No, keep the name, I just wanted to show you my version.
That is part of 3d printing, the unlimited possibilities we have.