The ridges run in line with the 3 foot length of the panel.
The Amerimax Project Panels are 3 feet long, by 26-1/2 inches wide. With the overlap they cover an area of 36x24 inches. If you want 10 foot panels you need to look at ROOFING panels, not project panels that are really not intended for roofing.
Answering early in morning with no tape measure and it raining outside. Looking out the window, I am estimating. I will say 3 to 3 1/2 ft. These were decent sized.
Each panel is an overall size of 36 in. x 26.5 in. The 36 in. is in the direction of the corrugations. With the overlap between sheets, it covers a 24 in. wide area.
Some Home Depot stores will cut it to custom sizes, some stores don't. Contact your local store. This metal is easy to cut, you will need a pair of tin snips, a circles saw, or a saber saw, all of these will cut it nicely.
As the ad says "Panels come in a pack of 3"