Thanks very much for the replies. It's not really what I want to hear! This is for a professional application so I need to make a full-sized machine (2m x 1m x 0.2m approx) and I don't have time to make a smaller prototype. If I had tons of cash I'd buy a top end 5-axis machine, but my budget pretty limited, so it looks like a 3-axis self-build for me.

My problem isn't really the design as such it's the choice of parts. I can use SketchUp and AutoCAD but that's not the problem. For example, given my desired machine size, one fundamental problem is to make two runners 2m long and 1m apart. These have to be absolutely level and parallel to each other. I need to know what type of materials are ideal for that and what kind of equipment and processes are used to install and measure them. That's obviously just the start. I read the CNC cookbook so I do have an idea of the various components.

I'm thinking that perhaps instead of 'plans' I should have said 'plans/kit'. I looked briefly at this site here:

www.cncrouterparts.com

And judging from their specs and few blogs from people who've assembled their kits, it looks good (any views?)
One issue is that they are US-based, but they would ship to the UK for a cost. Perhaps there is a company in the UK like that?

In summary: not a huge amount of free time, limited budget, large-ish machine for commercial use.

Thanks,
Woodspiral.