dangerous bathroom leak

Okay so for months my mom has been noticing that when I take a shower, there's some water that pools on the hardwood floor in the entry hall beneath the bathroom. And she berates me for letting water get on the floor and not pulling the curtain closed all the way. But I do dry it up as soon as I get out. Anyway, tonight, I went down to take care of my laundry and even though I had not been in the bathroom for several hours I looked up and there was a huge and I mean huge water stain on the garage ceiling, the storage boxes beneath were actually soaked and bits of the plaster had actually crumbled off. My mom shut the water off in the house, but the question is what do you recommend we do next? It has to be a leak in the piping, there is no way that a little water on the floor could possibly cause that.

OK, so you have an upstairs shower, a downstairs hall floor, and a garage most presumably also downstairs. Since we cannot see this layout and where and how the water would travel, it would be hard to give any good advice except perhaps to call in a plumber. The first thing you need to do is stop using the shower.

turnig off the water to the house is drastic unless you knoiw there is a leak . See if the little dial or triangle on your water meter is moving at all. If not, the leak is DRAIN related.

Water on the floor can find a seam or go under the apron of the tub or a baseboard. ( Caulking all those is a good idea, after you figure this out) It could also be a leak on a shower valve or the shower head pipe, or the shower drain. More detective work is needed

a couple of things i have run into over the years. i have had the arm for the shower head split on the threads and leak water inside the wall when the shower was on. when they started making tub spouts with an o-ring for a seal i also ran into a few where the installer was a little careless and when they shoved the spout on the end of the copper caught on it and pulled it out of its groove so when you pulled the rod up to make the shower come on the water squirted out the back of the tub spout inside the wall. i have had instances where the gap between the tub and floor or wall and floor wasn't caulked and water would run under the tub or baseboard and leak down below. if you check for a leak like jimbo suggested and don't find one there try filling the tub halfway and draining it and see if water shows up. if not it narrows it down a bit. how old is the house? I've seen bad solder joints go after a while also.

As mentioned there are a LOT of places where water could come from, and do not assume it was too little to cause the puddle you see. Unless the water is dripping 24 hours a day, it is NOT a pipe leak and turning off the water will not cure it, other than to make it impossible to use the shower so it cannot leak, assuming that is actually where the water is coming from, and you, nor we, know that for a fact yet.