I didn't know you could lift a sailboat with a roof over it. The cut out would have to be as wide as the spreaders or nearly so, wouldn't it? Also, if it's on pontoons it would be subject to wave action. How does that work?
the cut out (by eyecrometer) is about 6x8, most of the roof is removed on the front half over the boat.
A lift mounts on 4 arms that swing on the sides of the dock slip. the pontoons or floats are mounted on a frame with bunks that attach to the arms. the arms pivot at both ends. the arms keep it all parallel to water level. Each pontoon has a big air line going to it and a hole in the bottom. on the dock is a blower and a control valve. to lower, open valve, water flows in the hole in the bottom sinking the floats. to raise, open valve and turn blower on (high volume, low pressure) it blows air through the air line into the float displacing the water and raising the lift.
nearly all boats here are on lifts, just not usually sail boats due to the keel though. this merit, being swing keel is an exception. Across the cove is an s2 7.8 on a lift as well. that's the only 2 sailboats I've seen on lifts.
I can get a better pic of a boat off a lift, or the lift out of the water if you want to see it in more detail.