It’s an interesting project there. I got curious, so looked it up on Google Earth. And found no 3D model around the area except Elland Road, the succor stadium. You all SU user around Leeds needs to fill it in man.
I made a quick study:
Few textures from the web were added. The mill is about 122 meter by 67 meter with ceiling height of 10 meters. That makes each domed section about 11.5 x 11.5 meters. The sky light opening comes out at around 4 meter diameter. So, most of the soil weight for the grass roof was sitting close to the columns. Good thinking. The building is sitting on sloped ground; the ground at the back of the building is about 2.3 meters high.