How to Make a Flat Cement Roof

Remove old roofing, if present, down to the battens of the structure. Dispose of any old materials in accordance with local regulations.

Fit preformed concrete tiles to cover the battens of the structure. Begin in a corner and work in rows to create the roof from the preformed tiles. Use a measuring tape and concrete cutter to fit the tiles around chimneys or other protruding objects in the roof. Place the tiles completely flush with one another, leaving no gaps or spaces.

Mix quick-drying concrete in a wheelbarrow with a shovel or in a concrete mixer according to the manufacturer's directions.

Spread a thin layer of the quick-drying concrete over the preformed tiles. Spread approximately 1-inch of the mixture with a shovel and smooth with a trowel. Allow to dry according to the manufacturer's standards. Do not continue with the project until the concrete is dry. This might take up to 24 hours.

Cover the roof area with polymer modified bitumen membrane. The product comes in rolls and is available at construction and home improvement supply stores. Apply a polymer-based adhesive to the roof area using a paint roller on an extender handle. Roll the membrane sheet smoothly over the adhesive. As you unroll over the adhesive, use a push broom to smooth the membrane.
Work in rows, with each subsequent roll being flush to the previous, leaving no gaps or spaces between the lines of membrane. Use tin snips to cut the membrane to fit around drains, vents or other protruding objects.

Cover the roof area with small gravel. Spread approximately 3-to-5-inches of small construction grade gravel over the entire roof with a push broom.