walls lined with same chipboard you make boxes to size of your loft but allow space to manover them depending on how big you want the boxes internaly i choose 10 inch as thats the size of a nest bowl , the 1ft was decided as can get 4 1ft x 8ft strips off a 8ft x 4 ft sheet of 3/4 chipboard so your my fist measurement was 10 inch i drew a line then i added another line 10. 3/4 inch , then another at 20.3/4 and so on , half of the slot is removed either by router or by jigsaw and chizzle they simply slot together and brackets to hold it together it is realy simple