The original Anglo-Indian word bungalow, inside the UK is always a one-story house. The OED, with entries from the 17th century says,
Orig., a one-storied house (or temporary building, e.g. a
summer-house), lightly built, usually with a thatched roof. In modern
use, any one-storied house.
Outside of the UK, bungalow is often applied to a single or dual story house, where the second story is beneath the eaves, as @1006a has commented.
However for UK purposes, single story, is bungalow, any detached domestic residence that is more than that is called simply a house. Often people will say things like do they live in a house or bungalow?, expressing a distinction in the terms.
However, just to avoid confusion, the word house also tends to be used as a generic term for any domestic residence, where the nature of the structure is not known to the speaker - e.g. Do you watch much TV at your house? It could be a house, bungalow or flat in a sentence like that. It would be unlikely anyone would say Do you watch much TV at your bungalow? -even if it was known that they lived in a bungalow.
A flat in the UK is a residence with a shared front door, and common areas with other similar residences. It can be on any number of floors.
A semi-detached house is one that shares a party wall with a neighbour - so it is two houses in one structure, each with its own door. A terraced house is one that is in a row of three or more joined houses in a terrace.
A maisonette is chiefly a British term (also Australian) and expressed by the OED as A part of a residential building which is occupied separately, usually on more than one floor and having its own outside entrance.