| Structural demand | Heavy; wants engineered support | Timber/truss, lighter loads | Lightest | Roof + wall-coping detailing |
Flat concrete roof (reinforced concrete slab)
The choice when: the plan genuinely uses the deck, a terrace, a future floor (the structural considerations guide covers the floor-above case), or an urban plot where outdoor space must go upward.
What it demands: engineered design (it is a structural slab, not a lid), falling to outlets, the falls are the drainage and they are decided in the drawings, not on site, and a waterproofing system that is understood as a maintenance item with a service life, not a one-time purchase. The classic failure is the flat roof built dead-flat: the membrane was never the problem; the water standing on it was.
The honest costs: the highest first cost of the group, plus a recurring waterproofing cycle, and the lowest wind and storm exposure of the group. Buy it for the terrace, not for the fashion.
Hip roof (four slopes, no gable ends)
The choice when: the default pitched roof, bungalows, duplexes, any footprint where clean drainage and wind resistance matter (hips shed wind better than any other shape; no gable end faces a storm).
What it demands: slightly more complex carpentry than a gable (the hip rafters and their fixings are the skilled part) and a well-detailed ridge and hip capping, every hip line is a water path to be capped properly.
The honest costs: moderate; the premium over a gable is carpentry time and capping metres, repaid every storm season in drainage and wind behaviour. The workhorse choice for a reason.
Gable roof (two slopes, triangular ends)
The choice when: budget and simplicity lead, simple rectangular plans, extensions, low-cost builds. The simplest carpentry geometry of the pitched group, the least sheet cutting, the fastest build.
What it demands: gable-end bracing (the triangular wall takes wind load the hip never sees), correct verge detailing where sheets meet the gable, and the same ridge discipline as any pitched roof.
The honest costs: lowest of the pitched group, with the caveat that the saved carpentry money is repaid in wind exposure on the gable ends, a fair trade inland, a poor one on an exposed coastal or hillside plot.
Parapet wall styles (flat silhouette, hidden pitched roof behind)
The choice when: the aesthetic is the brief, the modern "box" silhouette, commercial frontages, estates with a design code.
What it demands: the most detailing of the group: the hidden roof behind must still drain (through box gutters or concealed outlets, a box gutter is a maintenance item with a name), the coping must shed water clear of the wall face, and the parapet wall itself is masonry on a roofline, it cracks if the structure under it moves, and it is the first place water finds a bad detail. Every concealed component is a component you cannot inspect from the ground.
The honest costs: moderate-high first cost, and the highest inspection discipline of the group. A parapet style without a maintenance plan is a design that ages badly on a schedule.
The Selection Logic: Four Questions
- Does the plan use the roof surface? Terrace or future floor → flat. No → pitched family.
- What does the plot's wind do? Exposed plot, storm belt, coastline → hip. Sheltered inland → gable is fair value. Parapet only with the maintenance commitment.
- Who inspects it, how often? A roof you can see from the ground (pitched) forgives; a roof you cannot (flat, parapet, box gutters) demands a calendar, before every rainy season, the outlets, the gutters, the coping.
- What sits under it? Rooms below a west-facing flat slab need the insulation story solved; rooms under a ventilated pitched roof get rid of the day's radiant heat every evening. Comfort under a hot sun is mostly a roof-geometry outcome.
The material question (stone-coated vs aluminium vs. long-span vs. concrete) sits inside whichever type wins the geometry, the type decides drainage and heat; the material decides cost profile, colour retention, and fastening method. Match the fixing to the material's instructions and the laps to the pitch, and remember the roof test that outranks every brochure: the hose at the ridge before the final payment (see foundation to roof).
The Cost Picture: Planning Reality
Ranked honestly for a typical residential footprint: gable cheapest of the pitched family, hip a modest premium over it (capping and carpentry), parapet styles above both (detailing, coping, concealed drainage), and the flat concrete deck highest of all, a structural slab plus falls plus a waterproofing system with a service life. But first cost is only half the picture: the pitched roofs are close to maintenance-free for their first decade; the flat deck and the parapet's box gutters are subscription roofs, cheaper only in years they are inspected. Run the sheeting and timber quantities for pitched options with the roofing lines of the build-to-roof estimator, and price the flat deck as a structural slab in the structural calculator rather than as a "roof", because that is what the building is buying.
The Pre-Rain Ritual: the Roof's Maintenance Calendar
Whichever roof type wins, its behaviour over decades is decided by a calendar, not a material brand. The ritual that keeps roofs alive is a single annual inspection, done before the first heavy rains (roughly March):
The walk. On the roof (flat/parapet) or from the eaves with binoculars and a ladder-check (pitched): debris clearance, leaves and dust hold moisture against every surface they touch, and gutters and outlets blocked by dry-season dust become waterfalls aimed at the wall at the first rains.
The lines. Ridge caps and hip cappings (pitched): re-bed what the sun has lifted, a ridge cap failure is the most common leak there is, cheapest to fix before the rains and most annoying during them. Flashings and box gutters (parapet/flat): every junction is a water path; a gutter is a pipe pretending to be a wall. Outlets and falls (flat): ponding water is a design or blockage failure, and standing water finds membrane defects with mathematical certainty.
The underside. The stain audit from inside the rooms below, ceiling stains are the roof's diary, and every stain is a leak that has already happened once. Caught in March, it is a repair; discovered in August, it is a room.
The flat and parapet roofs demand this ritual religiously; the hip and gable forgive a missed year. Price that difference into the choice, the subscription is not the membrane alone, it is the annual hour.
Conclusion
A note on the decision's timing: the roof type is decided at the design stage, not at the roofing stage, the parapet's coping and the flat deck's falls are drawn into the walls that will carry them, which means the wall-plate heights, the beam sizes, and even the downpipe routes are already roof decisions by the time blockwork starts. The most expensive roof conversation is the one that happens after the walls it needed were built wrong for it.
Choose the roof as a system, not a silhouette: flat decks for plans that use the surface and owners who inspect; hips for the exposed and the sensible; gables for the sheltered and the budget-led; parapets for briefs that accept a maintenance subscription as the price of the look. The rain, the sun, and the wind will read your choice every season for the building's life, choose for them, and the appearance looks after itself. And when the choice is finally made, hold the roof to the only standard that matters on a stormy night: tested at the ridge before the final payment, clean at the outlets before every rainy season, and detailed at every junction the drawing took the trouble to name.