While the Farmers store will be the dominant feature, the complex will also include 12 new retail stores, with these fronting both the Avenue and Maria Pl.
The building will surround a 71-space carpark.
"Every shop will be accessible from the carpark or via an enclosed walkway linking it to the Avenue, giving customers a one-stop destination for all their shopping," Mr Efstratiou said.
He said the style of the development would reflect and complement the streetscape "in keeping with that of a small city such as Wanganui".
He said materials and colour schemes had been chosen to reflect neighbouring properties and blend in with the area.
The contract is scheduled to be completed by November, with the first stage including the major store and carpark and the second stage taking in the retail stores.