How many bags of material do I need for a 9x6ft shed base?

Just buy a ton bag of ballast it's a lot cheaper. If you're not sure on how to calculate you would be best off paying a professional in all honesty.

You will need 0.90 tone and 8 bag of cement. From building merchandise the weight will be average 0.80 tone s

I would use 20mm gravel.

If it’s just a shed to store general gardening tools etc then a 4” concrete base will be fine. You’ll need 1 ton of ballast/concrete mix and 10 cement. That will cost around £110 or less depending on the building suppliers. If you’re planning on having a shed built with brick/block etc then you’d be better with a 6” concrete base. You’ll need 1.6 ton of ballast/concrete mix and 16 cement. Rough price £180. You’ll have a little excess materials left over. Easy enough to dispose of.

Ballast (bulk bag) would be the cheaper option. You would also need 7 bags of cement. This is based on 4" (100mm) depth