However funny it sounds, it's not that funny for me. As long as I could lock the notebook itself away in my room at home, it wasn't a problem. But now, temporarily, I've to move to a student dorm where I'll be living with three other students in a very small room. The privacy issue is obvious. The desktop wallet is in my notebook's HDD.
How may I build a secure system from any relevant online and offline threats?
Privacy isn't your concern... with 4 people living in a small room, you have none. Security is your problem!
If you don't feel that you can trust your roomates:
1. Secure your OS... in this case, maybe Windows isn't your best option, perhaps Linux is a better option. In either case, a strong password is your first layer of defense.
2. Secure your wallet... at the very least a strong wallet password... or perhaps an encrypted partition to store the wallet on
3. Secure your laptop... perhaps a lockable container of some description... may not stop complete theft of the container itself, but it might deter any opportunistic types