Hello,
I am doing same thing - got prusa mendel and building rostock printer. I choose rostock because I don't want spend $ on aluminum extrusion.
As for guide - I didn't seen any I based on sources found in [
www.thingiverse.com] and I plan to use fishing braid lines not belts [
www.thingiverse.com]
Also I wanted to use printed rods - so I use: [
www.thingiverse.com] - if there will be problems calibrating etc. I'll consider change.
I printed all parts and ordered 8mm rods 36inch long with LM8UU bearings x6. this makes printer pretty high - but I plan on extending bed size and extra height will be needed.
I also got new electronics - ramps 1.4 which I didn't connect yet. I choose ramps because I got that already on my prusa mendel (I plan on keeping original prusa mendel intact for printing parts as needed).