If I was to build my own PC

[Iuck]

Would I need an Optical Drive?

 

[Alpha3031]

No, unless you needed to use CDs/DVDs/BluRays

 

[Rationale]

That depends on what you use the PC for.

 

[Iuck]

Would there be a gap where the optical drives meant to go?

 

[Rationale]

Would there be a gap where the optical drives meant to go?

No. If you don't add an optical drive, cases have plates meant to fit into the empty slot to cover it.

 

[Alpha3031]

Most people don't use ODs these days, but it could come in handy in an emergency. That said, it will also take up 5.25" bays you may want to use later.