plumbing question

....to correspond with the Architect's drawings?

Typically if your going through the wall with a P-trap then 18".

If the plumbing is subfloor as in a suspended floor then you can install the p-trap and run straight down.

18 inches as stated in another post, but make sure you consult the local plumbing code for any variances from the national code.

YES!

YOUR LOCAL BUILDING INSPECTOR !

Different sinks have different depths. Some are deep and some are shallow. If you installed sinks so that the drain height above the floor is always the same, counter heights would be non-standard and standars cabinets would not fit or the toe kick would be a nonstandard height and would look funny. If you start from the counter height for standard cabinets whether in the bathroom or the kitchen and they are different, spec your sink, you will find out what that dimension will be. However it's really not important. Fortunately contractors and their plumbers have been installing counters and sinks for quite a few years and will install everything in a standard way unless you pay them extra to be different. You would be advised to do the same yourself or you will find extra costs to do things in a non-standard way.