Aren't telescopes easier to buy than to make?

Yes. There are a lot of good instruments available to buy, but telescope makers are looking for something else. They are looking for understanding and mastery. When you've made a telescope, a malfunction does not mystify you. And like anything else in a hobby, it is a way to kill time.

What kind of telescope do amateurs make?

Amateurs almost uniformly make Newtonian reflectors. These are simple telescopes with one curved element (a big mirror) that are tolerant of errors, very good performers, and relatively inexpensive.

Do they make or buy the main mirror?

Some make and some buy. If you don't currently have a telescope, and you are thinking of making rather than buying, then buy an already-made smaller mirror. Then, while you are making the mirror on Scope #2, you are not under pressure to finish it early. Haste makes poor glass.

What is the easiest telescope to make?

A 6-inch f/8 is good, and it is the traditional first telescope, but I would recommend an 8-inch f/6 or f/7 as an alternative (like the Lionel motto: "big toys for little hands"). If you are not making a mirror, a 10-inch f/5 is possible and easy.

I've seen all of these 16-inch and up telescopes. Can one of these be my first?

They can, but if you are a beginner there are ergonomic issues that may blindside you. Best to make your first errors on a smaller telescope and gain the design experience.

What does ergonomics have to do with telescope design?

It is the difference between a telescope that is a pleasure to use and a telescope that will break your back. And I'm not referring to carrying it, either. The availability and angle of the focuser and finder, whether the eyepieces are at hand, whether you must stoop over or stand on tiptoe, or whether the telescope is easy to balance can all be important. This is one of the most neglected topics in telescope making.

Do homemade mirrors give better images than commercial ones?

In general, no. Homemade mirrors can be better than commercial ones, but they are not better because they've been "loved." They are better because of the experience of the telescope maker and the amount of time that can be devoted to the project. First mirrors are usually terrible. However, that does not mean the commercial one is necessarily good. Deal with reputable makers who are willing to present test results, and be prepared to pay much more for a good mirror.