Expansion joints for 10m x6 m shed

depends on a few factors: compaction base laid, steel - amount and size, soil, concrete thickness ......

My 10x4 shed slab I didn't bother based on the concretor's advice. I'd put in a crap load of steel and off cuts (reo sheets) and its not got one crack in it 2 years later.
So perhaps take some advice from your concretor.
If you need to run an expansion cut with an angle grinder, wait 5 to 7 days as it will be too soft and chip as you cut it.