When you book a hotel room you need to decide which room you choose. If you book a room during the peak period (busy season, high season), you are charged a rack rate (the price which is advertised), but if you decide to come in the quiet period (out of season) you are likely to get a discount (you pay less).
Usually hotels calculate prices on the basis of two people per room, e.g. a room for 100EUR. If you wish to stay there alone, sometimes you are charged more than a half of the regular price - you must pay a single room surcharge or a single occupancy supplement.
You are to choose one of different types of rooms. These include not only single room - a room with one small bed or double room - a room with one large bed. Other types are: twin (a room with two small beds), triple (a room with three small beds) or a family room (usually to accommodate four people, one large and two small beds). If you are alone, you may stay in a studio - a small room with a sofabed. Some rooms, especially suites (series of separate rooms and a living room) contain a king size bed (a double one which is longer and wider than usual). Suites sometimes are called a junior suite (smaller one), a presidential suite (the largest in a hotel) or a honeymoon suite, a.k.a. a bride & groom suite. When you stay in a hostel you often sleep in a dormitory - a large room to accommodate several people. If a bathroom is attached to the room, we say that it is en-suite.
Beds, as the vital facilities in hotel rooms include apart from a single bed, a double bed or a king size bed: a bunk bed (or simply bunk) - two beds, one over the other, a sofabed, which can be used as a sofa during the day or a rollaway, which folds into a wall when not used as a bed. Rollaways are sometimes called Z-beds or Murphies (brand name).