Prevent puddling on patios
Standard engineering advice for "flat" exterior surfaces is that they actually be sloped at 1/8" per foot (which is close enough to 1cm/meter as to make either perfectly acceptable) for drainage purposes, rather than be "dead flat."

Method is to make the base that shape, using anything from laser levels to stakes and strings. The base needs also to be stable and compacted so that it stays that shape over time. Stability in cold climates may involve thick layers of well-draining material and sub-surface drains to prevent frost-heaving.&nbsp;