Hi, I need to level my garage floor. It's an old concrete garage on a concrete slab, 6m long by 2.5m wide. Over the years it's settled towards the back and now when it rains water collects at the back. It's used for storage so standing water is a problem now. To get the floor level I need to add 75mm at the back which will give me a 12mm lip at the front to try and stop water ingress from the drive. In total I'm looking at about 1 cubic meter which I'm hoping to mix on site with a borrowed mixer. Would I be better to use a concrete mix with 10mm gravel or just use a sharp sand and cement screed or a bit of both? How many bags of cement/gravel/sharp sand would I need? If possible I'd prefer to use big bags rather than 25Kg ones for sand/gravel. There are no oil/grease stains on the current floor which is smooth and unbroken.