间
jiān
The counter for space cut out by walls: 间
The picture A pocket of empty space fenced off by four walls inside a building, reachable only through its one door. 间 counts one empty cell walled off inside; 座 counts the whole building that holds those cells.
Where the picture shows up in 间
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a cell to spend the night in
我想订一间房。
wǒ xiǎng dìng yì jiān fáng
I'd like to book a room.
Taking one key at the hotel desk and opening one door along the corridor.
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cells lined up along a corridor
这层有五间办公室。
zhè céng yǒu wǔ jiān bàngōngshì
There are five offices on this floor.
Five identical doors lined up on both sides of a corridor.
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the cell a patient sits inside
病人在那间病房。
bìngrén zài nà jiān bìngfáng
The patient is in that ward.
Pointing at one numbered ward door down the hall.
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a cell opened for business
我们在楼下开了一间小店。
wǒmen zài lóuxià kāi le yì jiān xiǎo diàn
We opened a small shop downstairs.
One bay of the ground-floor wall opened up with a signboard hung over it.
A large shop or firm takes 家 instead.
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the cell a lesson happens in
这间教室下午有课。
zhè jiān jiàoshì xiàwǔ yǒu kè
This classroom has a class in the afternoon.
Pushing open the door of an empty room holding only a board and desks.
All of it in one picture
The hotel room you book is 间, the five offices down the corridor are 间, the ward where the patient lies is 间. The little shop opened downstairs and the classroom with an afternoon lesson are, stripped down, each one walled-off cell too. 间 does not count what is inside; it counts 'a pocket of space closed by walls with one door in'. That is why a shop with a signboard and a ward with a bed can both be counted as a single cell.