What is the difference between Hookup wire and Building wire.
Are they same
If so then why call hookup wire

Please elaborate your question stating size of wires used enabling us to answer.

Wire is wire for the most part, but there are differences.

But, let's take something like 14 AWG hookup wire and 14 AWG THNN.

The THNN has an approval to be used as building wire. That affects insurance.

The THNN has a plastic overcoat. This makes it more slippery. It resists abrasion when pulling through conduits etc.

Insulation does affect the current carrying cabaility and so does the ambient temp and location.

When you look at a building, there are lots of wires used. You could have fiber, coax, CAT5, doorbell, Thermostat, fire alarm and "building wire".

Solid wire is cheaper and is good to use within the building.

Colors are important too.

Tstat wire has a brwn jacket and is solid.
Fire alarm wire has a red jacket.
CAT5 cable should be colored coded based on it's application. A riser, main feed and connections within a floor get different colors.

But, the biggest difference is the resistance to abrasion and it's "approved" for that use.

In reality all wire has approvals.