A person who enters buildings illegally is commonly referred to as a "trespasser." If the individual specifically breaks in to commit a crime, they may also be called a "burglary suspect" or "burglar." The terminology can vary based on the context of their actions and the laws of the jurisdiction.
A hacker tries to access a computer illegally.
You would call that forgery on a black market and the person selling it a con artist.
A builder.
builder
An architect.
An architect
An archaeologist or an architectural historian typically studies ancient buildings.
an architect designs a building
Dealer, supplier or distributor...
Security guard
If you are here illegally, he can. If you are here illegally, he can.
...is illegal I can only do so much with incomplete sentences.