teresahaveago said:
How do I work out how many boards I need? Where do I measure?
Measure the area you wish to have covered with the boards.
Measure the loft end to end and side to side, then times the measurements by each other.
ie: if the distance between the side walls is 5 metres, and the distance between the front and back is 6 metres, 5 x6 = 30 square metres. Just mention this to the shop where you buy the boards from and they'll work out how much you need.
Make sure they will let you return any unused, in case they work it out wrong, or try to sell you too many. Get them to confirm.
The loft panels sold in B&Q are ok, but they also sell 8x2ft lengths of chipboard, specifically for flooring. These are much more economical but slightly trickier to work with, due to their length. Expect to pay about £5 per board...and pick up a couple of dust masks while you're there, but not the thin papery ones.
If budget is tight, you may just want to board off just a section of the area. Under the eaves (the edges where the roof meets the walls) can be tricky to fix down do to lack of height to work in. So you may wish to leave these as they are.
Hope this helps, let us know when you've got the stuff and are ready to continue.