I agree with Phil, you will not save any money by building your own boat.

I built a 14. I had all of the expensive parts (Carbon mast, sails, lines, blocks) already and most of the construction materials (Fiberglass, Carbon, kevlar, etc). I spent $1500-$2000 on just little stuff. I estimate I would have spent ~$6000-7000 if I had to purchase everything at full price.

Keep in mind there will be a big difference in final cost between a 14, 16, and a 18. Look at the factory prices. Unless you have some parts laying around, you will not spend much less.

In terms of time, I would estimate the platform represents less than 1/2 the total time. If you include integration and getting things to work, building and finishing the platform is about 1/3 of the total time.

I sail a 14 and a A-Class. I like the 14 because I never feel that I am overpowered by it. Even in 25+ kt winds I never felt overpowered. I was in danger of being beaten to death by the ocean but I had control of the boat. Compared to the 14, the A-Class is a luxary rocket ship. There is no comparison in performance and I can do everything without help. I do start feeling out of control at 15-18 kts and it takes a lot more effort to sail than the 14.

If I didnt want to build and wanted a boat I could sail by myself I would consider an older A-Class with a high wind/reduced area sail.