Agree with @dohraime, look at next size up. I always buy the next size up in quilts/doona covers as well, so there is a bit more overhang on the sides.

if you want to be able to open the doors, load the boot and walk around i think you need at least 9m x 7m but if you to also want useable work benches and storage spaces (eg for the lawn mower etc) add at least 1 m to width and length

Um, why? Looks difficult to clean, difficult to access, and impossible to safely bath kids. I would avoid at all costs. No prospective real estate buyer ever said "I love the combined bath and shower arrangement" as they are generally universally hated, especially if there are toddlers, or elderly in the household . If you do go with this dangerous proposition then make sure you have plenty of well anchored grab rails so you don't knock your teeth out when your head hits the floor. Have a look at the Posh Domaine Shower Bath, which has a flatter, squarer base, rather than your traditional bath Best of luck, Dr Retro of Dr Retro House Calls and Dr Retro Virtual Visits.

If you are with a project builder, they will be able to organise all of this as that is what they do all the time. They will know what is and what isn’t feasible on this piece of land. So.....once you decide on your builder then get them to draw up designs that suit you and the land. Since it is an unusual block and needs access for the easement, then an off the shelf design may be a problem. You will need a project builder to design a home for this land, which a lot of project builders do. They have buying power for building products so it’s an excellent way to build your home. Why pay for a surveyor now, then the project builder will probably do it again at your expense.