The eradication of homelessness by using the freely available naturual resources available to the governments of the world, including slate, stone and wood, could be used to build houses for £20,000 or $20,000. Houses are currently being built for £20,000 / $20,000 by companies already.
The problem is caused by governments paying near full price for houses to be built, and housing homeless people in overpriced accommodation, where landlords know the rent will be paid by the governments of the world at overinflated prices.
The Governments of the world need to take back the building process into their own hands, and use robots to prepare stone and make bricks, and lay bricks rapidly.
Those people interested in building their own houses could be sent on Government courses.
Also the communities of all countries could help build houses together as communities, the same way the Amish currently do, the same way they build barns etc.
The Governments of the world have enough land to build houses for all the homeless people.
Applying this solution could save the world roughly £26 trillion.