hi, i have prepared my shed base in my garden and now i am about to lay a sand/dry cement (researching on this site i have read people using a 10 parts sand to 1 part dry cement mix).
i would like to know the following if anyone can help me please:

what type of sand/cement should i use?

how much do i need for a hole which is 10 ft by 10 ft and approx 4.5inches deep?

do i need to protect the walls of the hole with wood? (i havent and it seems fine but im curious all the same=)).

many thanks in advance=)

chris