OP; Realistically you might want to look for a builder with more patience than I would have... FWIW, I have a few old left over quad butted tubes that have lots of Left Karma, we should use two of those in the design and use tubes with the moderale Top Karma for the rest of the frame to keep it all balanced...[;-)
Realistically, suggest riding several frames until you find one that is pretty close to perfect in the non-measurable areas and take it with you to your session for discussion with your builder. Well before hand put your riding style in writing and at considerable depth then add a list of the component you will add, the required braze-ons, etc. Be descriptive, not directive. I'll note that dictating the tube type and model up front may result in the builder having to make compromises elsewhere in the design and not be able to meet all your needs... Recommend also being aware that the time the builders spends talking with you has an hourly value. FWIW, I normally would expect to spend about 90 minutes in the shop to capture what a customer really wants out of a frame assuming they bring it in with them and stays focused... After that the cost of the frame has to start to go up.
Hope that helps...and please note that I am not poking at you on purpose.
/K