Well, if you are a talented frame builder, go for it. Or pay someone serious $$ to build one. Of course, you really need to know the size and the geometry first. You are really pretty far from being ready to have a frame built.

+1 you are pretty normal sized. Start testing out 52 and 54 cm bikes. Look harder, they are out there. I have probably found at least 50 bikes in that size in the last two years, and passed on 50 more.

+1 The beauty of buying used (assuming you do not overpay) is that if you change your mind later, you should be able to get most if not all of your money out of the bike. Buy one new, or have a frame built, and you will be losing serious $$. I upgrade all the time, I have yet to have lost money on a bike I let go.