Conversation so far:
When did the Gaelic Ireland settlements begin?
Square and rectangle-shaped buildings gradually became more common, and by the 14th or 15th century they had replaced round buildings completely.
What did they replaced the Gaelic Ireland round buildings with?
Square and rectangle-shaped buildings gradually became more common, and by the 14th or 15th century they had replaced round buildings completely.

Question: Who did the designs?
Self-contained rewrite: Who did the Gaelic Ireland architecture designs?