To attach the sheet I would firstly mark onto the sheet were the centre beams are so I know for later were to nail. So I firstly I draw around the whole frame with PVA glue, this will give the flat some extra hold all the way around instead of just the nailed parts. It takes two really to lay down the sheet accurately I line with the frame. If the sheet is slightly out or doesn’t quite fit then it can be routed later but I will come on to that later. Once everything is lined up we were ready the either pin or nail gun together the flat with the frame. To do this well you need to start at one end do all the way along, next along both sides and finally finish at the opposite end that you started at. This will ensure that the wood wont bow or go off centre.