Good advice from all. Choosing a tree is, in my opinion, is the most important part because what is best for the horse and rider is a lot more important than what the saddle looks like. Of course quality is important, but who makes the tree is less important than fit for horse and rider. I am in the middle of making my third saddle, and experienced makers helped me decide on a tree. Looking at many, many custom saddles online and in person, and choosing the parts of those saddles I like best, has helped me design the saddle I want in the end--I think. I am sure there will be many details I would have done differently. The experience of making a lot of saddles is probably the only thing to reduce regret about the saddle you make. It is also ok to copy a saddle you really like. I used cheap poster board from walmart to use for making patterns, but beer cases work just fine too. I also have discovered that after coming up with a decent pattern using cardboard, using vinyl from a fabric store helps me make the pattern for the seat because it bends and flexes decently, and assists in a final commitment to the seat cutout.
Another thing to consider is finding a mentor or a saddle maker who is willing to offer good suggestions as you make it. leatherworker.net is an outstanding source, absolutely, and wish I had found this site before I started making my first. I am amazed at the work of both amateurs and pros. But I was really reluctant to start the first saddle because it seemed such a huge undertaking. It is a really big project for a first time leather worker like myself. I went through two makers before I found one that let me make my own saddle, and not a copy of one of theirs. The saddle maker I finally found--by shear luck in a hardware store--showed me how to make each piece. The result was First Place and Best In Show at the 2007 New Mexico State Fair. My second saddle, made from scraps mostly, was a christmas present for my girlfriends daughter, and the third I am making now is my beater saddle, which I think is going to be nicer than the first. My girlfriend has fallen in love with my first saddle. I love it in an arena and working, but not on the trail for long periods. #3 will likely be my favorite. I will try to get some pics of #2, but it is going to be a while because I am working out of state.
First saddle:
http://good-times.we...551651511rPBbpl
Third saddle:
http://s959.photobuc...apaint/saddles/