Takeoff Studio Pro
Click inside a room and Takeoff Studio traces it to the inside face of the walls - one room or a whole floor in one go. On drawings exported from CAD, Auto walls finds the walls and measures them along their centre lines, with the doors and windows counted.

Set the scale from a dimension you trust, or read it from the title block. One-click area and Auto walls both need the page calibrated.
Choose Room on the toolbar (or One-click area in the command palette, Ctrl+K) and click inside a room. It's traced to the inside face of the walls and shown as a preview. Shift-click more rooms to add several at once.
If the fill runs out through a doorway or a gap in the walls it turns red and isn't added: raise Close gaps and click again. Wall to wall measures to the walls whatever is drawn in the room - furniture, kitchen units, baths and door swings.
Click inside a preview or press Enter. Tick Make rooms to add them as numbered rooms, ready for heights and finishes. They're ordinary area markups you can edit, and each Add is one undo step.
Choose Walls, set the range of wall thicknesses (75 to 450 mm suits most plans), then Whole page or Draw area. Click any wall, door or window to leave it out, then Accept all. Each wall becomes a polyline such as Wall 100 mm, and the doors and windows become counts.

Help: Tools has every option in detail.
Part of Takeoff Studio Pro. Measuring in Takeoff Studio is free. Pro is £24.99 a month or £199.99 a year, the first month is free, and you can cancel any time from your Microsoft account.
Yes. It works on scans as well as CAD drawings, as long as the page is calibrated. On a scan it follows the solid walls.
No. Auto walls reads the drawing's line work, so it needs a PDF exported from CAD. Scans and pictures have no line data to read - measure walls on those with the Length or Polyline tool.
If the fill leaks out of the room it turns red and isn't added. Raise Close gaps - it closes openings up to that width - and click inside the room again.
Yes. The rooms are ordinary area markups: drag their points, add or delete points, add cutouts, or undo the whole Add in one step.
One-click areas and Auto walls are part of Takeoff Studio Pro (£24.99 a month or £199.99 a year, first month free). Drawing areas and lengths yourself is free.

Floor, ceiling, wall and skirting quantities for every room, with totals per finish and level.

One measurement becomes every item it needs. Then an Excel bill in NRM2 order with live formulas.

Lay the new issue over the old one. Every change is boxed, listed and ready to cloud.

Box one socket or light and every match is found and ringed for you to check.

Voids out of areas, joists and studs at centres, repeated rooms and pitched roofs.

Scale from the title block, scale regions, the drawing register and text search.
Measuring is free. Takeoff Studio Pro is £24.99 a month or £199.99 a year, and the first month is free.