I am interested i building my own antennas like to start with a 2meter
dipole.
My questions is, say you have a plan that says to use 1/2 inch copper.
How do you know what will happen if you use thicker material like 3/4
inch tubing? Is there a formula that shows what the effect will be? Or
maybe efen smaller diameter? Or what if you use solid material instead
of hollow tubing.

What if you use the same diamter but a different material, such as
stainless steel instead of copper or aluminum instead of copper?
Please forgive these questions if they seem basic as I am a beginner.
My guess is the thickness of the element is not as important as the
spacing between elements but this only can be true to a point. I mean
for arguments sake what if you used large sewer pipe? I would guess
that would not work too well.