I am planning to deck alfresco with concrete flooring. It has got a clearance of 120mm. The concrete is not perfect levelled and in some places it could be 125-130 mm clearance.
I am planning to use Merabu timber is 19mm thick. So, I am left with 101 mm to work through. I was thinking of a minifoot (Builders Edge 25-40mm Minifoot Pedestal Feet - Bunnings Australia) and top it with 70 * 45 joists. I see that having 90*45 joists and leave a clearance of 10mm (and ti could be more where it is uneven) could be an option too.
Welcome to the Bunnings Workshop community @rajavamsi. It's brilliant to have you join us, and many thanks for your question about constructing a low-level deck.
Both of those options could be considered, and each has advantages and disadvantages. Using the 70mm timber allows a larger gap under the timber, which will assist with airflow through the structure; this is important to prevent the early onset of decay, especially if the deck is exposed to the weather. However, you'll need more supports as 70mm timber can't span as far as 90mm. Conversely, you'll require less supports for the 90mm timber, but there will be less of a gap under it for airflow.
Given that this is already a very low-level deck, I suspect the additional airflow gap under the 70mm timber won't benefit much. Using the 90mm might be the most straightforward solution.