Do u have to use cement I think not, I think alot of slabs/bricks been laid now are straight onto sand in between slabs/bricks you could put a dry/wet your choice mix in which will help keep slabs/bricks in place for you to walk on, so say you make a mess just take them back up then get someone in to do it for you, if you watch alot of the garden programmes on tv they do put slabs/bricks on to a sand base only, a little tip also is when sand/bricks is ready for slab/bricks you could sprinkle a little dry cement on sand base before putting down slab/bricks this will make it a bit more solid when you walk on it