Start with how you'll use the deck — dining, lounging, a path, a sun-trap — and let that set the size and position. Watch where the sun falls through the day, how you'll get to it from the house, and where water currently drains, since you don't want to dam it. Sketch the footprint to scale and check it against the space and your budget. A deck that's slightly smaller but better placed beats an oversized one squeezed into the wrong corner.

A ground-level deck sits low, close to the soil on pads or shallow supports — simpler, quicker, and the right call for a flat or gently sloping garden. A raised deck stands on posts set in concrete footings, with beams carrying the joists and diagonal bracing keeping it rigid; it's the answer for sloping ground, for matching a raised threshold, or for a deck that needs to be at first-floor level. Raised decks also bring in railings, steps and — potentially — building control. Decide which you're building before you price anything, because the two have very different material lists and labour.

For the substructure: pressure-treated C16/C24 structural timber for joists and frame, 100×100mm posts for raised decks, concrete (post-mix or ballast and cement) or pads for footings, joist hangers and framing anchors, and structural coach bolts or screws. For the surface: your chosen decking boards, correctly specified decking screws, and fascia/edging boards. For protection and ground: weed membrane and a free-draining sub-base, a DPC strip if fixing to the house, joist protection tape, and end-grain preserver for every cut. For finishing timber decks, a decking oil or stain once the boards have settled.

Tape, pencil, set square, a long straightedge and a long spirit level (a line or laser level helps on bigger decks); string line and pegs for setting out; a spade and post-hole digger or auger for footings; a circular saw and/or jigsaw plus a handsaw; a drill/driver and an impact driver; a combi or SDS drill for masonry if you're fixing a ledger; spanners or sockets for coach bolts; a pilot/countersink bit; consistent board spacers; clamps; and knee pads. Most of this is standard DIY kit; the footing tools and a good long level are the items people most often lack.

Mark the deck footprint with pegs and string, and prove it square by checking the diagonals are equal. Clear turf, roots and vegetation, dig out soft spots, and roughly level the area. Lay a weed-control membrane and a free-draining layer of gravel or sub-base so water drains away rather than sitting under the timber, and consolidate any made-up ground so it can't settle later. Before any digging, check for buried services — drains, pipes and cables can run shallow near a house.

A low ground-level deck can sit on level concrete pads or slabs spaced to support the frame just clear of the ground. A raised deck needs posts set plumb in concrete footings — commonly around 450mm deep in firm ground, deeper in soft or made ground — braced temporarily and left to cure before loading. Set footing and pad positions to suit your beam and joist layout so every member lands on solid support. Footing depth and post sizing for raised decks are structural matters worth getting designed or checked on tall or sloping sites.

If the deck abuts the house, a ledger board bolted to the wall carries one edge of the frame. Set its height so the finished deck surface sits at least 150mm below the building's damp-proof course, fit a DPC strip behind the ledger, and bolt it securely into solid masonry — not just render — with corrosion-protected fixings. Check it's dead level before final tightening, because the whole frame references off it. Never fix over or above the DPC, and don't seal the deck tight to the wall in a way that traps water.

This is the heart of the build. Construct the perimeter frame square and level (allowing for the fall), then hang the internal joists at the correct centres for your boards — 400mm for straight softwood, closer for diagonal layouts and composite. Fill every joist-hanger hole, keep all joist tops in one flat plane, add noggins to stop the joists twisting, and brace raised decks diagonally between the posts. Tape the joist tops and treat every cut. A frame that's square, flat, well-supported and rigid is the single biggest factor in a deck that lasts.

With the frame ready, acclimatise the boards on site, then lay them across the joists. Set a consistent expansion gap with a spacer (around 5–6mm for timber; the manufacturer's figure for composite), align the first board dead straight, and fix into every joist — two screws per joist on boards over 120mm wide to prevent cupping, kept back from board ends. Land every end join on a joist and stagger the joins brick-bond for strength and looks. Check the run stays parallel every few boards. Composite often uses hidden clips or specific screws — follow its installation spec.

Run the boards long, then trim the overhang in one pass to a chalk line for a crisp straight edge. Treat every cut with end-grain preserver, and fit fascia boards around the perimeter to hide the board ends and frame and shield the timber from rain. Once a new timber deck has settled and dried, apply a quality decking oil or stain to feed the wood and help it resist water and UV, reapplying periodically. Composite needs no oiling — a wash down is generally all it requires.

Any deck raised enough to fall from needs railings (balustrade) and, usually, steps for access. Posts for railings are best planned and fixed into the structure during the frame stage so they're securely anchored, not bolted on as an afterthought. Steps need their own firm footing and stringers tied back to the deck. Railing heights and the spacing of balusters can be governed by Building Regulations on raised structures, so check the requirements that apply to your deck height before building these — this is a safety element, not a decorative one.

Because the ground prep and footings end up hidden, they're the first things people skimp on — and the cause of decks that sink, tilt, sprout weeds and go out of level within a year or two. Clear and consolidate the ground, lay membrane, and give raised decks proper footings to a sensible depth. The time spent here is invisible in the finished deck and absolutely visible in how long it lasts.

Deciding to lay boards diagonally, or switching to composite, after the frame is built leaves joist centres too wide to support the surface properly — and the result is a bouncy deck. Board material and direction must be chosen first so the frame is set out to suit them. The surface dictates the frame, never the other way round.

A dead-flat deck holds water; an unventilated frame sitting in damp air rots; and bare saw cuts let rot in even on treated timber. Build in a slight fall, keep the structure clear of the soil and ventilated, tape the joist tops, and re-treat every cut. These details cost almost nothing during the build and are the difference between a deck that lasts a few years and one that lasts decades.

Building a raised deck without checking whether it needs permissions, without adequate bracing, or with inadequate or non-compliant railings is a real safety risk — and can mean rework or worse down the line. Check what applies to your height and structure, brace raised frames properly, and treat railings, baluster spacing and steps as safety-critical. When a raised structure's stability or compliance is in any doubt, get it designed or checked rather than guessing.