Some of what I have built here is copied from other youtube videos. Special thanks to...        http://www.youtube.com/user/DonFrambach    ..... who did a much better job on his frame. I just used fixed castor wheels with no bearings.
I simply blended everyone's ideas together. The rare earth magnet resistor I built has a cable and thumb lever adjuster to operate while riding the bike. This has given great control. The aluminium roller does NOT get magnetised. The magnets set up an Eddy current when the roller spins and this in turn slows the rotation.
When I get  fitter and have more practice, I look forward to really hammering it!  I have a fan set up for cooling as Sydney winters aren't that cold.
Total cost over and above original roller trainer is around AUD70 as I used scrap timber lying around home. I only had to purchase the castors, magnets, bolts, cable and thumb lever. Next I am going to add a flywheel to create some  "roll on" for even more reality.
Sorry, I can't provide any plans as all roller trainers…

I added rare earth magnets to my rollers to create resistance and it works great.