Do I need fabrication drawings?
If a fabricator is making steel for your project, then almost always yes. Engineer's calculations tell you the beam sizes; they don't tell the fabricator how to make and connect them.
Fabrication drawings give the shop the exact lengths, holes, notches, welds and connections, plus marks so each piece is identified on site. They also let fabricators quote accurately rather than guessing.
For a simple single beam a builder may work straight from the calcs, but anything with connections, posts or multiple members benefits from proper fabrication drawings.
Structural sizing, spans and load calculations must be carried out by a qualified structural engineer. These pages help you plan the drawings you need - they are information only and are not structural engineering advice.