Question about CAD and 3D software

Hey guys…got another question.

I’m interested in working with CAD and 3D room layout, or whatever you might call it. I want to create 3D rendered models of rooms for interior design/structure design.

Does anyone know of any openSource or freeware software for CAD(architechture/structure design) and openSource or freeware software for 3D design/rendering specifically for use with CAD design?

Not sure if you all know what i mean. If you’re still clueless let me know and i’ll try to elaborate.