Little details make for a successful project. Little mistakes make for disasters that are hard to overcome. Here is the proper flashing detail for a window.
Here is the result when proper flashing is not done after only a few years.
A lot of time and effort is put into detailing drawings to get the little things right, but there is no better guarantee that it will be right than to have the architect perform Construction Administration, a reputable contractor as part of the team, and an adequate budget to achieve the quality desired.