I built the C-Beam machine, like @karaelena, from a kit supplied by OpenBuilds, http://openbuildspartstore.com/c-beam-machine-mechanical-bundle/ I had no problems following the YouTube video produced by Mark Carew of OpenBuilds https://youtu.be/HVR8pABCHXI.
I did have to buy a controller, steppers, and power supply, but that gives you the option of choosing your own if you are familiar with a different control board or already have a power supply or steppers.
The machine works well, my only problem is that I have a Makita trimming router which is a different body diameter to the Bosch Colt and despite shimming the mount it has some “slop” I need to get rid of. I have not been able to machine aluminium successfully yet. My first project was to machine a router mounting clamp to suit the Makita … yeah, no … didn’t work. I’m keeping the broken mills and mangled aluminium to remind me of the problem.
The machine works well with wood, I’m even considering trying to make a router mounting bracket out of hardwood. I would also follow @karaelena and install an aluminium base plate.
I should say that I bought the machine to introduce me to 3D modelling, G-Code and CNC while I was waiting for the GF. It has certainly done that!