Thanks for sharing your question about the Colorbond shed. Cutting down the walls of the shed to fit into the space is possible. However, before reaching for the cutting torch, I just want to make sure that you've exhausted all possible spots for the shed. Once you start cutting it up there will be no going back.
The shed size will be based on the roof size of the shed. If you look at your birds-eye view drawing, you'll want the roof line about 100mm away from the fence line. This is so that the rain will fall inside your area and not in your neighbour's garden. If your shed is attached or right next to your house. It will need to be 2700mm on the righthand side, 2890mm for the front, same size for the left side of the wall which is 600mm and 3000mm. However, the last part at the very back will need to be 740mm.
I would double-check the measurements by cutting out some cardboard and placing it on the floor to make sure you are not near the fence. Once you've verified the measurements, you can start cutting the walls. A good deal of modification will have to be carried out to the sidewalls so that the wall corners will seal properly again.
Let me tag our experienced members @TedBear and @Adam_W for their recommendations.
If you need further assistance, please let us know.