Here are some pictures of the space I have been alloted for my model railway fantasies:

Thanks for those thoughts David. Someone else also suggested I get water up there, so I'll definetely be sure to ask for a sink area, turn it into a proper workshop area.

The entire house is in a similar state, the whole beauty of the concept being that it is the purchaser that decides how the interior is to be redone based on the purchaser's own needs.

We'll be hiring a personal architect to redo the entire house from top to bottom, so there'll definetely be a fixed staircase installed that will connect all floors (at the moment there is no staircase)

They've redone the entire roof, and indeed have installed new windows, after heavy rain there was no sign of any new leaks or anything so that's already a good sign.

Will definetely be sure to ask about isolation - though I suspect a good deal of work has already been done in this regard.

In terms of lighting, would I be looking to install halogens or so?

Aside from just after the velux windows to the walls, I'd say the rest of the space is one where you can remain standing. 

Sounds ideal! Will need to read up on it!