Prospective contractors given until 12 May to prequalify
West Ham has invited bids to become contractor on the £100m transformation of the Olympic stadium.
The successful contractor will overhaul the 90,000 capacity venue into a stadium capable of staging football matches, athletics events and concerts.
Procurement for the design and build job will be handled by Legacy Stadium Project, a joint venture between West Ham and Newham council.
Works include the extension or replacement of the existing stadium roof to cover the majority of seating, building hospitality boxes and toilets. The brief also includes offices and a new community athletics warm up track.
Legacy Stadium Partnership expects to let the contract in August and has proposed a May 2014 completion deadline.