Thanks for the reply.
I can understand that MDF or birch ply might not be the most ideal material to use but from reading quite a few build logs - it seems as if a lot of people build a cheap router out of stuff they can gather together - it works albeit a bit roughly - then use that to make new parts for an upgrade :)
You're right about steel but I don't have the gear for welding or the money for aluminium at the minute.
I do have the facilities for machining timber however! and thought that making a timber one would highlight the problems etc. that can arise on a build.
The running gear can always be swapped to a shiny metal new one after I would hope :)
I'm only looking for a machine to rout ply's and mdf anyway with not a great deal of accuracy .1mm would probably be fine,although I would like to do some 3d carving so I expect I'd need it better for that.