The most common and most likely answer to this crossword clue is the 7 letter word ROTUNDA
I've seen this crossword clue in The Daily Telegraph
R
O
T
U
N
D
A
More clues leading to the result ROTUNDA
- Decay reported beneath the Pantheon, for example
- Building’s bar area storing large quantity of beer?
- Do a turn, roaming circular building
- Crazy to reverse during new road building
- Break out and run round building
- Barrel in middle of road smashed into building
- Decay reported beneath the building
- Building with bar area keeping Hazel back?
- Barrel kept in bar, a domed building
- Radius sorted out — and altered circular construction
Buddy explains!

The straight part
We know that "round building" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case round building = rotunda.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ROTUNDA mean?
ROTUNDA noun- A round building, usually small, often with a dome
- (frequently capitalized) A Gothic typeface used in early printed books in Northern Italy, based on a rounded script developed in the 13th cent.; the manuscript hand on which this typeface was based
- A roundabout; a road junction at which traffic streams circularly around a central island.