Making 3CP Maps

Im mainly interested if anyone has any particular methods for creating 3cp A/D Gravelpit style maps? Having tried a couple of times, starting from the first two points and expanding from there, I have come to the conclusion that the best way is probably to start with either blue spawn or red spawn/3rd point and expand from there instead.
So far, these are all the areas I am aware I need:
-Two control points
-A set of connecting rooms between the two
-A third control point
-Connecting routes between 1st/2nd and 3rd
-A forward spawn for blue
Just interested to hear your thoughts...