In Britain we have a very distinctive building tradition influenced by native developments and the peoples who've pass through here.
The most ancient of these is perhaps the "Celtic" roundhouse which have existed here since the Bronze age and probably evolved from tee-pee like tents in my opinion (as still used by the Nenets of Russia).
In most areas the roundhouses were made from a post frame and wickerwork with wattle and daub walls and a thatched roof. In upland areas such as Dartmoor they had stone walls - hence why those in Dartmoor left so much evidence.
In Scotland, parts of Wales and Northern England they placed roundhouses on artificial constructed islands in lakes. This lasted in Scotland and Ireland the latest and there's a fine reconstruction on the Tay. These were called Crannogs.
Roundhouses were also constructed in NW Spain.
Tents like this could have evolved into roundhouses:
Most were round, but not all.
Again, I'll mention that these existed before Britain was Celtic but the Celts carried them on. They would have also had rectangular buildings alongside them too, but roundhouses were prevalent and would be so until the Romans.