ok, i've got a real keyboard and a few minutes, let's see what I can remember....
mine was 8x12, 3 sheets of plywood worth. I used 2x4 on edge framing, and then used 2 2x6 on edge as the lifting bars (these ran under the entire layout from side to side and extended a few inches out from under the edges. The lifting ropes/pulleys attached to these.). Thin plywood since it doesn't make it any stiffer, and more cross members 'cause they do....
1st you need space above the opened garage door. I had a very tall garage so it worked. Remember, the layout has to lift and fit in the sapce above the garage door as it opens! This space has to include the lifting ropes and mechanism and hills, crossovers and scenery on the layout! Mine had almost 3' above the garage doors to hold the layout.
So assuming you have the 'headroom', let's talk about the mechanics.
The layout is heavy. Very heavy, deadly if it falls on someone and major damage if it falls on a car. You need something to hold is securely when it is suspended. Lots of cross supports to make it stiff and not flex too much. Plaster scenery is not a good idea. Foam and papier mache is flexible. Hint, hint.
For the lifting mechanism, I used a hand crank boat wench bolted to across 2 studs in a wall...spread the load. 4 ropes ran to it from 4 lift points. Mount it low enough on the wall where you can really put your back into it. It's a workout....
On the ceiling were 4 double pulleys, and 4 double pulleys on hooks that attach to the layout. double pulleys mean that the weight of the layout is spread over 4 lengths of rope. Your muscles will need to lift 1/4th the weight of the layout. It means that for every inch you lift the layout, you will wench in 4 inches of rope from each lift point (or 16 inches for every inch you lift). Get a big wench to hold lots of rope....
The ceiling lift points were suspended from eye bolts, not lags. The eye bolts were attached to 2x4 cross pieces in the attic, each of which were layed across 2 joists, so that each lift point was loading 2 joists, not just one! The eye bolts were secured using large fender washers to futher spread the load. Double nuts locked the bolts securely.
As security, I added a 2nd set of ceiling lift points (using 2 different joists) and attached a short loop of rope. This loop was looped over the ends of the 2x6 main supports when the layout was fully lifted. This allow me to remove the strain from the wench when it was suspended above my car...I had a long stick to manuver the rope loops in place once it was up there.
If I made any errors, I erred on the side of over-engineered...I am an engineer so it comes honestly...
I used this layout for a couple of years, but a southwest facing garage and S Texas summers conspired to minimize the enjoyment.