It is likely he is being charged with First Degree Criminal Trespass, as he is being accused of trespassing inside a building. The maximum penalty is one year in jail, a $5,000 fine and two years probation. If the prosecutors believe he was intending to commit another crime while inside, he could be charged with the class C felony of Second Degree Burglary, which carries a standard sentencing range of up to 90 days in jail (assuming this is his first felony).
Regardless of whether he is being charged with a misdemeanor or felony, he needs to retain an experienced criminal defense attorney right away.
I agree. Criminal Trespass in the First Degree is a gross misdemeanor. Maximum sentence is 364 days and or $5,000 fine. No statutory minimum sentence.
If you are the same person who posted the other questions about adverse possession, then the larger concern is the Residential Burglary charge, not the trespass.