Found it difficult to get a supply locally of green bean but suggest 918 Coffee Company (click on their logo above)  they are very knowledgeable, have a wide range of beans,  will ship 1kg quantities for the DIY'er and are reasonable on shipment costs

Coffee Roasting

I  had a long illness last year with some spells in hospital. Boredom set in and during a trip to the tip to get rid of some cardboard I spotted a discarded popcorn machine. Hence began my interest in coffee roasting. here is the set up so far.

I have separated the control of the heater element (rated 1200watt but I calculated about 1100 watts based on the resistance of the coil - 1100w/240v=4.6amps) and the fan to give more control. Actually I adjust the fan speed to give a "fluidised bed" to the beans (so they float and move around in a fluid motion) and then just leave it. I wired out the dropper part of the coil intended for the DC motor via the rectifier diodes (if you leave this connected in series, you will reduce the power by increasing the overall coil resistance). Lots on the web so won't repeat it here. Use a 5amp fuse in the plug and a RCD if you don't have one on your house circuit

I fitted a larger triac (8amp) to an old -well built  (had a big choke already fitted) light dimmer and screwed it to a small heat sink from a scrap motherboard. I managed to find a cheap PWM motor controller on Ebay for £5 (could not make it for that) and ran an external laptop psu at 19v through it (never throw away wall warts/psu's!). 

I then replaced the initial mechanical thermometer with a cheap scrap PID unit where one of the led segments had failed. This was not programmable so no use for setting the ramp of temperature but I used it with a K type thermocouple to monitor the chamber temperature. 
I found an Alba DVB decoder box at the Tip (they are a miserable lot) and took out the PCB's and used it to house the parts for the controller. I wish I could find more, but all the housings for such things are now very low profile as the designs get more and more integrated.

Results have been far better than I imagined, but getting repeatability has been the issue. I have now bit the bullet and ordered an Arduino but I'm nervous about the programming, as the last time I did any I used punch cards at University! Any help would be gratefully accepted.

Update not much luck with the Arduino, but managed to find an obsolete Pixsys AT242 programmer with a rudimentary ramp programme for £20. Have now fitted it to the roaster and wired a SPDT panel switch so I can switch from the Triac heater control to the Pixsys as necessary. also fitted a 25amp SSR so I do not have to use the internal relay of the programmer. Still playing with it at the moment but hoping it may give me the repeatabilty I am looking for

If you have a programmer such as the REX C100 (either RKC or Chinese copy) with an output relay, I recommend you remove the relay and replace with 2 x 100 ohm resistors and use this 12v output to an SSR, they are very cheap now