Is it considered uncouth to go to a tailor and have him measure you, then not buy a shirt from him? I know if I measure myself for this site Ill mess it up, so ideally I would like a tailor to do it. Ill offer him some money, but Im pretty sure it will be awkward.
I highly suggest you not send them body measurements. Measure your best fitting shirt and tweak the measurements to your liking.
I've used Propercloth's (referral link in sig) body measuring and they got it spot on. Even offering three different sizes. My tweaks were very very minor. I was incredibly impressed with how accurate their computer got the measurements. Now, while I'm not entirely sure about how I feel about it, if you really want, you can put in your body measurements there, choose the fit you want, and use those measurements for moderntailor. But beware, MT asks for yoke and sleeve length, while PC uses a total sleeve length. Only difference IIRC.