Before putting down the insulation, fix noggins between the truss joists to support light fittings in the rooms below. Also, allow the electrician to complete the first fix wiring.

For hints on what tools you will need go to Hints & Tips - insulating the loft

Cut the insulation around any downlighters - your electrician will tell you how much space to leave.

If any part is to be boarded for storage etc. you will need to replace the glass wool insulation with cavity wall insulation. Check with your architect on the thickness to use, to ensure the SAP ratings are maintained. You may have to plant wood on top of the joists to give sufficient depth for the insulation. In the picture below, 20mm strips of wood were planted onto the 75mm joists to allow for 80mm cavity insulation.