Round, ring, or curcular?

[Dianova Olga]

Please, tell me the difference between these adjectives. What is the best way to use them in order to describe the object?

round square/
/ring road
curcular building

[Mister Micawber]

A 'ring road' goes around a city or city centre; if that is what you are referring to, that is the correct name for it.

A building would be circular if its floor plan is in the form of a circular. Tennis balls are round. A roundhouse is a building peculiar to train lines.

I don't know how 'square' fits into your thinking here.
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Native English teacher at Mister Micawber's

[Dianova Olga]

I mean the town square can be round in shape when it is surrounded by buildings that form a ring round it.

[Mister Micawber]

I don't think so. You'll have to draw me a picture to make me believe that.
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Native English teacher at Mister Micawber's

[Beeesneees]

Hi Dianolva,
Even when a town square is surrounded by buildings, these tend to be built in straight lines, so the square remains largely rectangular in shape.
If a town has a square, then you can expect a rectangle.

However...

"Round squares" as you refer to them, are usually called 'circuses'. eg. Oxford Circus and Picadilly Circus in London, and this very famous example from the city of Bath in England:

The circular area closer to the camera is 'The Circus' whilst the semi-circular street you can see further away is "The Royal Crescent".
Here's a closer view of The Crescent.
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Cheers m' dears!