How long did it take to build the temple at Karnak?

Answer 1

Hundreds of years. It was never really finished a each succesive pharoah liked to add bits to the complex.

Answer 2

karnak was apparently built over a period of 1300 years. i suggest you look on the web sites for further information. this huge religious site is the largest in the world and different parts were built by different Pharaohs.the most famous part the hyperstyle hall was built by the famous rameses II around 3200 years ago.