concrete slab for garden shed, any tips??

Best option is a slab a cm or two larger each direction but with a step down so the walls sit in the recess.

Exact size depends on the construction and thickness of the wall panels, is there any specs for the particular model ?


Edit:
If it’s one of the Absco brand you can download the instructions that usually include slab dimensions.
https://abscosheds.com.au/installation/

Example
https://discountsheds.com.au/wp-cont...o_J15231FK.pdf