I made the decision to build a Cozy just days after I got my Private Pilots license. I flew some here and there at first. I even worked on my Instrument rating. After a while I started to get annoyed with spending $75 an hour for a C-172 knowing that in a few years I could fly my own plane for "free". I haven't flown in over a year now and it got me worried a bit. I let my medical lapse too.
After some hard thought I've basically decided at this point that there is no point in flying just once in a while, the expense is worth it. I've decided to build full time (full spare time, that is), and when I'm about done I will spend some money to rent, get current, then seek out a willing Cozy pilot to check me out for a few hours, then fly my plane and no more renting.
I'm glad I had my license first though. I'm very glad I did some Instrument training too. Both will give me better appreciation of what needs to be done, mostly with respect to the cockpit.
If I was still single and not a new Dad, and had more money, I would certainly keep flying while building. But with my time and money, I can only do one - so building it is. I figure the longer it takes to build, the greater the chance it won't get finished.
Good luck in your decision and building.