Pensive Grandad, you do have a right to be somewhat pensive about your proposed project, but with a little research and careful building you can achieve your desire to have a layout which can be raised to the ceiling in your garage.
My father a retired Civil Engineer built a lift away arrangement for our Mirror dingy when I was a primary school boy. We didn't have an equal lifting arrangement nor a winch, but we did have home made steel safety hooks to support the weight when not in use. It worked for about 20 years with no problems except the laminated timber beams required re-gluing as the pva had not bonded well enough to the kiln dried hardwood.
Firstly, you need to ensure that you have adequate means of support from the roofing members in the ceiling above the garage, and that these are located above where you wish to place the suspended layout.
Secondly, you will need to know the locations of wall studs so that you can fasten a winch to the wall as well as any counterweight arrangement you may incorporate. Make things as easy and safe to use as possible.
Thirdly, I would suggest that you design the rigging so that the layout can be lowered to and held within 2 or 4" [50 or 100mm] of the floor to provide maximum flexibility when making and or working on or removing the layout. This degree of flexibility prevents the layout from crashing to the floor in the event of a failure of the winch as well as allowing you to easily load the layout into a trailer or ute when it comes time to move.
Fourth, I would suggest that you fit either S hooks or D shackles to the rigging to make it safe and easy to disconnect the layout when in use as well as somewhere to tie up the rigging to prevent injuries and tangles. I really liked an earlier suggestion of using turnbuckles to provide for levelling the layout.
Fifth, I would suggest fitting spacer sticks to the sides of the layout to prevent anyone [ie energetic grandkids] from over lifting the layout and crushing it into the ceiling.
If in doubt consult with people experienced in building to ensure that the structure will be strong enough and the sizes of bolts and fasteners required.
The Layout Table;
If you look back at the April 2009 issue of Model Railroader you will find an article on making 'Waffle Benchwork" which is a great help and exactly what you need to utilise. Basically what you are making is a torsion box so I would suggest that you read up on Torsion Box construction as this is what you are going to make. Premade metal fold out legs will also make life easier just provide support within the torsion box where the legs are mounted and braced from.
Wikipedia quote; A torsion box consists of two skins applied to a core material, usually a grid or framework of some kind. The torsion box functions as a beam, but is considerably lighter than a solid beam of the same size without losing much strength. Torsion boxes are used in the construction of airframes, especially wings and vertical stabilizers, in making wooden tables and doors, and for skis and snowboards.
As a Carpenter I have made a 8 x 4 torsion box benchtop for a workfriends layout and I was surprised at just how much stiffer the layout was once the bottom skin was attatched. I also drilled a series of holes through the stringers and webs to facilitate wiring the layout in an orderly manner. I have made a number of torsion boxes now and can recommend them, but remember that the type and amount of glue used is critical.
I would also suggest that you make the scenery using lightweight materials to keep the total weight down.