These are scans of my construction log book.  They will give you an idea of what is involved in building a balloon.

While the number of hours to build a balloon was close to what I estimated, the number of hours I could spend at building the balloon was pretty low. I taught evening class during the spring, I chased storms during the spring and summer, my mom passed away in April, I had a garden and two yards to maintain during the whole process, and there were a bunch of other miscellaneous things that took time away from building a balloon.

My recommendation would be to build a balloon well before you actually need a new balloon. This will allow you to proceed at a leisurely pace so that building seems more like a hobby and less like a job.