What you are proposing is called a header. A basic header of doubled 2x10 (or sometimes called 4x10, and usually has 1/2" plywood in between to make up for width of 2x4 plate), can only support one floor and an unused attic/roof, and it can't span more than 5-6 feet. It needs 2 jack studs (studs that go under the header) and one king stud on each side of the header. Jack studs support the header and king stud contains the header. 2x10 header with natural wood lumber can't do any more. Engineered wood header (usually called LVL) can do a little more.
Support for this load must be connected by building materials that are solid and can't be crushed (no soft shims like cedar and no wet wood that shrinks dry). People sometimes forget that there is a space in the joist bays and sometimes even between the wall and plates. The load must be connected down to the foundation with no interruption.
You see that I'm beginning to write a book. In your case, I would suggest a lot more research/self education and a help from a builder/architect/building inspector/engineer.