I would only suggest that you write down what you want the machine to do, if it is thin, small and intricate, or heavy large pieces and stock profiles.
If very heavy stuff look at a cross-bow style unit if light then a bed style, but do you want water or air, consider what type of air exhaust system you may need etc.
There is a place in Sheffield that seems to make them, perhaps once you have done a list shop around.
Still think the cross bow type system would be better then a bed for this type of material
Is with an Oxyfuel set-up, but you will get the idea.
That could be a lot of weight to place on a plasma bed and a lot of space to be permenantly occupied so moving the work piece around and placing on supports and then being able to bring the cutter to the work would have benefits.
But all in all just my thoughts, what ever you would need a lot of work to pass through to justify the buy and running costs so if you are considering it you must require a lot of this.