3D prints keep suffering from warping
For ABS it will warp unless you build a heat chamber. 

That said the tricks to reduce warping come down to: 


Material, i.e. PLA is less likely to warp; 
Use a fan, it helps so much; 
Make sure you have temps calibrated well - Too hot is more warp; 
Use a raft. The Makerbot uses a raft and no heated bed; 
Make sure the room is not drafty. Having it by the window will result in warping; 
Adding a large brim also helps;
I find good ol' glue sticks work the best at keeping the print to the bed;
SMASH the first layer. This one is controversial. I personally do first layer at 130% and print speed of 30%. You get elephants foot sure, but it's on the bed real good.


Tom is right. It is very very hard to print that big of a piece without warping. That said I have done very large pieces on my Ultimaker, using a fan, glue stick, MatterHackers PRO PLA and no raft. But again that's on an Ultimaker. 

Note you can build a heat chamber pretty easily. Specifically a passive heat chamber.