There's almost no information here to work with? What size room? What size bed? Etc, etc.. With that angle I'd probably recommend a daybed with a pop-up trundle under it. It makes a king when you want it or two twins when you don't. They make horizontal murphy bed kits but you'd need at least 62"+ for a queen or 56"+ for a full. That's more than 5' away from the ceiling and floor junction.
So we know 45 degree attic walls are a 12/12 roof pitch. The OP mentions nothing about a knee walls.
So assuming that, the OP needs to build a dormer for the murphy bed or have the client buy a sleeping bag they can roll up when not in use.
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