Andy Street says he wants to assign new developments to brownfield sites where possible in a bid to protect the region's greenbelt.
The area covered by the West Midlands Combined Authority (WMCA) requires around 165,000 new homes over the next 15 years to keep up with demand.
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Former John Lewis boss Mr Street said: "How can it be right that greenbelt is used for housing at a time when right across the region there are huge pieces of brownfield land that have laid untouched for decades?
"There are at least 1,600 hectares of brownfields sites in the West Midlands, which is about the size of 2,000 football pitches.
"This is why as Mayor I will commit to a 'brownfield first' policy. I pledge to make this a reality in the first case by using the WMCA's £200 million to get brownfield land ready for housebuilding and commercial use.
"We can't say that greenbelt can be protected permanently. But before we even think about using it for housing, we need to exhaust every other avenue."
Mr Street said he would prioritise getting brownfield sites back into use quickly, with one option being to secure funding to reclaim lands that may be contaminated.
"We also need to turn our attention to the 10,000 homes in the region that are currently unoccupied," he added. "We need to put more energy into this process and bring them back into use.
"We need to think harder also about the density of our housing, particularly in the towns and cities where the essential infrastructure already exists.
"And we need to look at change of use of some buildings – for example, we need to look at how we can make empty office blocks available for residential.
"We also need to work with neighbouring authorities – many of whom have land they are looking to develop for housing – to ensure we can make effective use of it.
"Yes, the housing challenge in our region is an important one. But people value our greenbelt and it's an important part of our quality of life.
"That's why I am committing here and now to doing everything we can to protect it, an outcome which will only be possible through a coordinated approach across the region."
Mr Street is running against Liberal Democrat Beverley Nielsen, Labour's Sion Simon, UKIP candidate Pete Durnell and the Green Party's James Burn.