Hey Peter,
Alexs Gliderol motor will not run your roof successfully. They simply arent stong enough or have enough throw to open completely.
If you are going to use a panel door motor use one of these
http://chamberlainanz.rtrk.com.au/?s...535&kw=1049565 scroll down to 230t, they are almost indestuctable, unrefined and hugely overpowered. In the industry they are know as the tractor, they use a 240v motor instead of low volt dc like most motors now utilize. I have installed around 3-400 of these and I have never had a powertrain failure. That says a lot. They also come with a extension kit to run upto 4m throw. I use a lot of different motors froma lot of different companies, so I guess I'm trying to say I'm not biased toward a single brand.
I dont use them anymore due to the low frequency hum (ac motor) and lack of features and no soft start. I actually use the mt60 and mt1000 dc motors for my garage door installs, but for your situation the 230t is THE best motor to use.
If you want the controllability mentioned by bassnut use on of these
http://www.ata-aust.com.au/shop/?fus...o&ct_id=97&i=5 go down to the 24v model slider. This is the almost the same motor that I used at the gco web site I linked to earlier. This features seperate inputs so you dont have to setup relays/megadata and stuff, Its all built in to the control board. And it has so many features that are SOOOOO handy for an observatory(gco's system shuts automatically on rain, wind over a threshold, internet loss. It is completely internet controlled). The ata gate motors are reliable too, although their warranty service leaves a little to be desired.
Feel free to give me a call.
Brett