How to get sized for home-built bike??
 

I'm going to order a frame and gruppo/build kit, but I'm curious...how does one figure out what size parts to get? Specifically, I'm referring to crank length, stem length, stem angle, handlebar width, etc.? I primarily commute on a mountain frame and am moving to road, so the measurements from the mountain bike really wouldn't transfer over here.

Do you just go to a local bike shop and pay for a fitting session? I didn't know if this would even work well since since they wouldn't have my actual frame to judge by. My fear is ordering a number of parts that turn out to be the wrong size.

Any advice would really be appreciated.