My main deviation from the plans was to lose the twin front doors and use the end wall. The kit comes with 'front' and 'back' doors (don't go there...). So a hole 27 x 12 was hacked in and a slimmed down 'back' was set in an open position. Above this a 10x11 hole was removed at attic level and a section of one of the large windows, which were otherwise spare, was bolted behind it.
The three main walls fixed at right angles and reinforced with the little semi-translucent strips which I took to be corner braces even though they look like something you put in your mouth when you get your teeth X-rayed. Note the chimney at one end and the Tip-ex used as a filler as I had nothing else to hand.