How to make a part that fills the volume of a region3?

I'm trying to make a part where the corner is one specific position, and the other corner is a specific position in a region3 (which forms a cube for a part to fill), anyone know a function/algorithm to do this? If it's a algorithm, make it something like this, so it's easy to understand:

function partFromRegion3() -- Returns the size and position of a brick
    -- do stuff here
        return position, size
end