First concrete 4 foot lengths of scaffold tube in to the ground at 5 foot centres the quantity will depend on how the finished tunnel will be. These tubes should be 3 foot long above ground
Next fix scaffold planks to the outside of the poles on both sides and the back using builders Band
Next put the 50mm water or gas or gas pipe over the scaffold tubes and push down to the top of the scaffold boards to create the hoops for a 10foot wide tunnel use 19 foot lengths
Next build the frameworks at both ends using randomised cls timber from Wickes or B+Q
The hoops need bracing on the smaller tunnels I use 2x1 timber
on the larger ones I use the same cls as the framework just screw the wood in to the pipe
you are now ready for the sheet
you can find the sheeting instructions here