is it possible to make your own electric kettle?

"Real world" engineers always take advantage of prior art. If you can buy a kettle commercially that will do the job, buy it. Then, you can give your full attention to the unique parts of your project.

It's not cheating. You should avoid "re-inventing the wheel" whenever you can.

That's not what you asked. But it's the best advice I can give.

I agree with Joe, not only is is more practical to use something you can get "off the shelf" it will be safer too considering that you said: "i don't know how to put it together"

If you chose not to take our advice, you should know that PVC is not well suited for temperatures at or above the boiling point of water, Stainless steel would be a fairly good choice but you may have difficulty with fabrication (another reason to use a commercially made kettle) Copper would be a possibility, it is relatively easy to work with, but even so, if you already had the metal working skills needed I doubt you'd be asking here

However Pyrex(tm) or borosilicate (generic term) glass would be a good choice for "the glass inside the case"