In my opinion, you would have a better chance in an interview if you reuse an existing engine such as Unity and make a game on top of it. You need to catch the interviewer's eye, and to be brutally honest nobody has the patience to look through more than a dozen lines of code.
However, *don't just make a game*. Implement complex things such as downloadable content, streaming level loading, online multiplayer, and cloud saves. Those kind of things aren't QUITE down-in-the-depths engine-level, but their complexity and importance is repeatedly underestimated by real-world teams, and they're rarely things that engines like Unity bother implementing well. If your interviewer understands this and you demonstrate proficiency in them with a portfolio you'll definitely catch the interviewer's attention.
But most importantly, be aware that whatever the interviewer thinks you're good at, likely will be what they make you do if they hire you. So if you don't like working on a particular type of system, don't show that off!
BTW, your English is fine.