that sounds great, I have roughly worked out how to pull the information from the model but im already hitting a problem

W = glazing - see problem below

A = thought of using a formula for either ceiling area and room area, or room area *2 then for the walls using the perimeter from room area * storey height

R = constant for most cases

T = constant for most cases

u = constant for most cases

M = constant

note about constants, they can just be changed on the fly, or within a parameter for the window family.

Glazing!

It seems that Revit is taking the area for glass/glazing from all sides, so it is well over.This is the equation

DF = MWuT/A(1 – R2)

Where:

W = total glazed area of windows or roof lights

A = total area of all the room surfaces (ceiling, floor, walls and windows)

R = area-weighted average reflectance of the room surfaces

M = a correction factor for dirt

T = glass transmission factor

u = angle of visible sky

Guide values for a typical dwelling with light-coloured walls are as follows (for more accurate values, refer to CIBSE Lighting Guide 10):

R = 0.5

M = 1.0 (vertical glazing that can be cleaned easily)

0.8 (sloping glazing)

0.7 (horizontal glazing)

T = 0.7 (double glazing)

0.6 (double glazing with low emissivity coating)

0.6 (triple glazing)

u = 65˚ (vertical glazing)