Is it something similar to the below you were looking for?
You can achieve this by adding the following attribute to the R( extension.
D(<offset from back or front wall (see notes)>x<offset from ground>;<door width>x<door height>;<side (F/B/L/R)>;<door texture>) or
D(<offset from back or front wall (see notes)>x<offset from ground>;<door width>x<door height>;<side (F/B/L/R)>;<door texture>;<door frame width>;<door frame thickness>;<door frame texture>)
Please note that currently a default door frame will be added if not set.
With regards to the <side>, although I am not sure about my logic behind this at the time I created this extension, the wall facing the side of the extension, in this case the right, will for the purpose of adding doors and windows, be classed as the front wall of the extension. Also the offset will be from the extension's right hand side.
In short, for an extension on the right, the right hand wall will be classed as F (front), the back wall will be classed as R (right) and the front wall will be classed as L (left). If the wall was on the left hand side of the hangar, the left hand wall would be classed as F, the front wall as R and the back wall as L.
At the moment these entrance doors do not have any details added to them, but I hope to change this, so it will use the normal entrance doors.
Please let me know if you need any more clarification on this or run into any issues.
Example used for the hangar below:
R(200),H(240),A(80),D(100x0;80x200;F;Silver metal)