The project for English Heritage will improve visitor facilities inside the ruined keep which dates back to the thirteenth century.
The practice , which is working with conservation specialists Martin Ashley Architects, won the job back in January 2015.
A timber structure will be installed to partially cover the ruin and provide a viewing space at roof level, while suspended metal walkways will give access to the buildings first floor level.
The structure of the new additions will rest on pad foundations designed to spread the loads without impacting on the archaeology of the tower.
A new single-storey visitor centre, which sits in the tower’s motte, will include an orientation space, shop, café, kiosk, and staff offices and facilities.
Clifford’s Tower is the largest surviving structure from the medieval royal castle of York which was an important seat of government of the North of England in the Middle Ages.
It was built on top of a tall earthen mound in the mid Thirteenth Century and was ruined by fire in 1684 and has stood roofless ever since. The mound is thought to have been created during the reign of William the Conqueror.
Jeremy Ashbee, Head Curator of Properties at English Heritage said: ‘We are investing in one of York’s most iconic landmarks to tell the fascinating history of Clifford’s Tower and its place in the city for generations to come in a way that’s never been told before. Getting an insight from the public will help us in reaching a decision on how we make these improvements to one of York’s most famous and beautiful landmarks. We want to make this a better experience for visitors and staff and we are keen to have the input of York’s residents.’