Moving onto the front door.
Sadly I dont have any pictures of the setup being made as it was raining and I didnt want my camera to get wet. The tarp I had up over the top all the way along helped prevent most of it, but i still got wet!
To make the front door, I clamped a piece of vertical wood to the inner sides of the space where the 4th wall would be, then I pretty much screwed planks onto that from the bottom upwards until I covered the opening. I did this as I was using scrap wood that I already had lying around. Then i put a piece of plywood across the top, attached some hinges at the back and at the front to make a upward folding design. This was all using scrap that I already had, so if your doing something similar and buying the bits, then you may do it differently.
Into the top, I put two bathroom ventilation fans to provide the suction in the theory that heat rises, and creating a positive flow of air, entering in the bottom, and exiting out the top. To put these in, I traced around the top of a bucket that matched the dimensions of the fans perfectly, then cut it out with a jigsaw. Then i cut a hole with a forstner bit next to them big enough to drop the power cords through so they are inside the box and out of the weather.
All the wood was given a layer of paint to help prevent weather and water ingress.