I buy my green coffee from Sweet Maria's...
They have a lot of information and tips for different methods.
The naysayer's tell you the Popcorn popper can't have the screen in the bottom...the chaff will drop down inside and catch fire.
Hum Bug.... I've been using one for almost a year now. If it's going to catch fire...it's going to happen because the chaff flew out...settled near the intake at the bottom of the air popper and was sucked in from that end. And that can happen to any of them. It's not going to magically by gravity fall down through a 25 mph breeze to get to the heating element.
Anyway. I use a Poplite...like:
Remove the yellow plastic top...but retain the measuring cup. Go to LOWE's or Home Depot...and pickup a 3" Glass Chimney and a peice of hardwood dowel. Go to the kitchen department store and get two mesh strainers with handles...and a hot glove.
You're in business.
Have an extension cord handy to plug the popper into. And all the other peices mentioned above.
Measure your coffee beans with the little yellow meaureing cup. It's about 1/4 of a lb I think. Pour them into the popper.
Place the glass chimney ontop of the popper. ( this keeps the beans from flying out while they're roasting...and if you keep the glass clean...it will allow you to watch the roasting.)
Stick the dowel down inside the chimney ( this is to stir the beans)
Plug your popper in...and quickly devote your time to stiring the beans with the dowel ( Make sure you're wearing a hot glove or the hot air will burn your hand)
As the beans begin to dry they get lighter...and really start dancing around in there. At that point you can remove the dowel...and then just hold the popper with two hands and gently gimbal it around to make sure all the beans get roasted evenly. Careful not to knock the glass chimney out while you do this.
The beans will start blowing off chaff (paper like outer covering) unless you've got decaf beans which have much less chaff. This stuff blows everywhere so you don't want to be inside.
Next the beans will start to darken and they'll reach "first crack" as the cellulose bonds break...it sounds like little snap noises. You'll hear it slow down for a little while or even stop for a while and then there will be a "Second" crack...which is a little shorter snapping sound at a noticibly different pitch. That's where I stop. It's in the range of Vienna roast. But you can go on to Italian roast or French Roast if you so please.
You'll get a hang for it after a while.
At the point you want to stop roasting...Quickly unplug the popper, remove the chimney with your hot glove hand, Pour the roasted beans into one of the strainers. Then transfer the beans back and forth between the two strainers.. This will allow them to cool rapidly and stop further roasting, it releases any smoke, and helps dislodge remaining chaff from the beans. WHen you're happy that they're not cooking anymore...put them on a paper plate to cool for a bit...and then into a valve bag to protect them from oxidation and to allow them to off gas a bit. Most coffee needs to off gas for 24 -48 hrs before you grind and brew with them.
And always prepare for the unexpected...just in case the naysayers eventually prove to be right...roast in an area that IF the popper does catch fire...you can unplug and walk away..and it won't destroy property or allow the fire to spread.
If you do a few batches in quick sucession...the thermostat inside the popper may trip. Unplug it and let it sit for 10 -15 minutes to cool...and it will reset itself.