Putting a vent in the ceiling open to the attic would be mistake. Although it would provide a source of combustion air for the dryer, it would seriously compromise comfort in your living space. In the winter it will allow cold or freezing air from the attic into your living space, during the summer you'll be pulling super-heated air in from the attic. You don't want to do this.

A better solution, if louvered doors are out of the question, would be a vent through a side wall of the laundry closet that opens into another room. Any vent will have to be fairly large, though (I'd guess somewhere in the range of 18" x 18"). Dryers move an enormous volume of air. A vent would need to be sized to provide unrestricted passage of whatever volume of air your dryer requires.

Thank you so much for responding. What you say makes sense. I don't see door style as much of an issue because the current doors (solid bifolds) are usually open when we do laundry so air isn't really a concern. But I am guessing the need for louvered doors or a vent probably has to do with code. If it doesn't, I can just leave the doors (or just the door in front of the dryer) open when I do laundry. Not a real biggie for the four-five loads per week that we do!

Your side wall vent is a good suggestion, but I don't know if it will work. To the right is the center hall of the house - can't really put it there for aesthetic reasons. To the left is the clothes closet in my bedroom (which has louvered doors!) but I am not sure that there would be any benefit to vent into this closet. The back wall of the w/d closet has the pantry and another bedroom closet behind it also with louvered doors.

I live in west central florida so we welcome any cold air that comes from the attic - it's usually hot air!

I suppose we can install a vent into the solid bifolds, right?