New greenhouse - this may take some time and you might get bored

As I’ve not seen your greenhouse, what type will it be? I’ve always fancied a Hartley Botantics, old JR is marvellous. 

Also as a spatial planner myself, I’ve got to know why does it stick out further than the other one.

I've just goggled the Hartley Botanics!  I wish!  Money and space no object I can't agree more, it's beautiful, but back to reality, the new one is a bog standard jobby, as it's a total extravagance I tried to keep costs to a minimum.  I've chosen a 6x8 Simplicity Shugborough which is one of the few high eaves ones that would go on soil.  Nothing beautiful but with the high eaves and some extra height staging it might make it less backbreaking at the work station.

As to why it's set forward... the grass path behind existing GH is near a hedge and quite narrow and not the easiest to mow and OH didn't want to narrow it even further. I want water butts to collect rain run off and the only place for them will be at the rear of th new GH.  So it's set forward to accommodate water butts.  One of the existing butts will be moved because access will be denied when new GH is in place, the other butt is a permanent one that 'leaks' water into the bed of GH no. 1 so stays.    As the whole garden is rather narrow, I think only about 15m, finding space in that area which allowed adequate walkways and mower access wasn't easy.