Tin Snips make cutting through sheet metal really easy. They contain a gear mechanism that allows you to exert the force needed to cut metal without straining your hands. You will use these very early on when you are adding flashing to your tiny house trailer and again when you are cutting the metal for your roof. They also come in handy on a few other miscellaneous jobs as well.
The Milwaukee Aviation Snip Set (3-Piece) performed very well in our tests. Marginally better than the more common WISS brand. You will want to get the 3 pack since each one works better in specific circumstances. They are color coded based on the orientation and angle of the blades which determines what curve direction they are best suited for. For instance, if you need to cut a curve to the left you would select the red handled version. This may sound like it would be difficult to remember, but when you are using them it is obvious which one works best.