So there are no safety concerns? - lock out switches, break beams etc to be worrying about.
(In the town where I live a kid once got killed by a blind style security door in a garage. sure he shouldn't have been messing about with it, but it should have stopped rolling down when there was someone underneath it!)
no mains will make things a lot easier too...
what you need is a motor (with gear box to slow it down and provide torque.
a battery case, and a double pole three throw switch. (the kind where the center position is off.
(you don't need a PCB at all!)
you'll have six points on the bottom of your switch.
1[Batt +ve] 2[motor] 3[Batt -ve]
4[batt -ve] 5[motor] 6[Batt +ve]
there is a little metal slider inside the switch, when it's in the middle position it just sits above legs 2 and five, push the switch the the right, and the contact pivot to the left, connecting pin 1 to pin 2, and pin 4 to pin five, the motor will spin one way.
push the switch the other way and it connects pin 2 to pin 3 and pin 5 to pin 6, this makes the voltage appear the other way around and the motor spins the other way around.
they seem to start on ebay at £1.26
DPDT On/Center Off/On 3 Way Latching Toggle Switch AC 250V/2A 120V/5A | eBay
or there is this one. (Probably not more than 30 minutes from your house if you're in the UK and Maplins are almost everywhere)
Everel 16A Momentary Rocker Switch (On)-Off-(On) DPDT Black | Maplin
it's got blue lights and everything.
(maplin also sells batter boxes and motors) - motors are probably cheaper out of china though, certainly ones with gear boxes.
you might want a box to mount your switch on to make it look good/finished? (but definitely no PCB!)