My machine would just about be able to do something that size (I think its maximum length is about 1400mm - although it could be put at an angle). Width and height are no problem (machine is designed to do 1200x1200x100, but can do more than that).

Three problems I can think of:

1) It would require someone to look after the machine while it's being made - and their time isn't free. How long it would take depends on the accuracy you need. This can't be you (since it needs someone who built the machine to realise that it's gone wrong).

2) Is it flat at the top/bottom (2.5D), or do both sides need to be machined (3D)? Also, are there cuts that need to be made to the side (4/5D)? 3D would be a lot more work, as it would need to be carefully aligned. And I can't really do 4/5D work on the machine as it stands.

3) It's not finished - when would you want it?