The gallery bosses are said to be in talks with Gavin to turn the 120sq m-wide roof space into a piazza-like area with decking and shrubs. Director Stephen Snoddy said: "We want a sexy design, but the project could take some time. It will be a trendy space, warm and inviting."
About 150,000 people visit the centre in the West Midlands each year to use the library and studio spaces. The centre was commissioned by Walsall Council, funded with more than £15m of lottery money and opened in February 2000.
Projected costs and building dates for the roof terrace have not been finalised as yet, but the design could be completed by 2009.