The place where I work designs such machines with beds always over 3m x 3m. I think the biggest bed that they do is over 10m. That might be a little small - not sure. But once you know how they work it's just a matter of extending out.
If you can find the plans online then you still need to know where to buy all the Steppers, controllers, steel parts and know what strength of steel to use for the beams etc.
Although I don't actually do any of the mechanical parts, I do know how such large format machines are made commercially.
So the skills to build this are readily available. There's Engineers available that if you ask nicely might do the SolidWorks designs. I know that something similar is available.
Even better, they might have some throwouts to get it started and some off-the-shelf components to start working with that are all commercially proven and tested in that exact type of commercial environment.