What’s the fastest way to start a new house plan?

Use New project on the Projects page. It asks for the site (plot width and depth, which way the road faces, and the state, which sets local building practice) and then offers a starting layout:

1. Pick a building type: bungalow, Kerala-style home, villa (G+1), apartment block, office or shopping complex.
2. Floors & Frames generates walls, doors, windows, stairs, finishes, furniture and the roof for your footprint.
3. Open it in the editor and change what you like. Everything is ordinary walls and rooms, so nothing is locked.

Tip: if you already have a hand sketch or an old drawing, use Trace in the 2D editor instead and draw over it.