An apartment renovation estimate differs from a new-build one in a single respect: you never fully know what is behind the old finish. That is why both a line-by-line breakdown and a contingency matter here, and both go in from the start.
By room or by trade
By room (kitchen, bathroom, bedroom) is easier for the client to read and to phase. By trade (strip-out, electrics, plumbing, walls, floors) is easier for you to buy materials and run the crew. In practice the best structure is sections by trade with the room named in each line: "tiling, bathroom, 18 m²".
What the estimate usually covers
Strip-out and waste removal (the skip is its own line, not "included"), electrics counted in points and metres of chasing, plumbing, wall and ceiling preparation and finishes, floor levelling, waterproofing in wet areas and coverings, doors, and materials listed separately from labour with normed consumption and offcuts.
Always carry a contingency in an older building
Crumbling plaster under wallpaper, a rotten timber floor under lino, aluminium wiring in the walls — none of it is visible when you price the job. A 5–10% contingency, spent only against agreed actual work, is the honest answer.
Pricing a whole flat "per square metre" is marketing, not an estimate: two 60 m² flats in the same building can differ twofold. Quantities are quick to get from our construction calculators; a ready form is the Excel template.