erecting a greenhouse

Can anyone help me?  I'm stuck inside with a broken leg - I have had a local builder/handyman putting in some raised beds for me... excellent - but I asked him to dismantle and collect a second hand 6 x 4 greenhose for me - he is now having trouble squaring the green house to start erecting it....any ideas??

Peter

if he is working on his own 3 4 5 it this is the foolproof way , measure 3 ft on the narrow end then from the same corner measure 4 ft then hold your tape across these to marks and adjust untill it says 5 ft on the tape that is a perfect right angle