What I will do better next time.

You live and learn.

• As I have said before, trying to cut the most complex frame first is a bad plan. But there are other things that can make life easier or more difficult.
  
  
• Never assume planks are parallel. If you want to cut a 3" strip of Oak, don't use the far side of the plank for your cutting guide. Rough cut planks are NEVER perfectly parallel.
  
  
• Cut long straight cuts with a circular saw, not a jig saw. Circular saws are made to cut straight lines.

• Working out of doors is a Pain it the . You have the cold, the dark, you have to take everything out and put it away. And you can't work if it might rain. Don't underestimate how much extra time everything takes if you work out of doors in northern Europe in the winter.

• Check the blade setting on your Jigsaw before you cut. Run it through a piece of scrap, take out a Square and make sure that it's cutting perpendicularly. It's a real pain to look at a frame you have just cut and realise that there's an unintentional bevel.

• If you want to use a guide or a
  jig with a Jigsaw, use blades with a set to the teeth. Bosch's T144DP does the job nicely, and it cuts Oak just fine. Blades without a set to the teeth tend to follow the cut, not the guide.