Assuming your roommate is on SEARCHABLE probation then I will tell you what my opinion is. Most felony convictions for drugs come with a search waiver, not all but most.
Probation searches are legal because they are considered CONSENT searches. The probationer gives PRIOR CONSENT to search in exchange from being free from custody. That means that the police or probation can search the probationers home, car or any area under their control.
What does this mean for you? First, you did not give prior consent. So to protect yourself get a lock for your door. Do not allow your roommate access to your room. Keep your door locked. Put a sign on your door that says, "I do not consent to a search of this room by police or any government agent". When police do come - IF they come, if asked to search you should tell them "I do NOT consent to this search and protest any search" HOWEVER DON'T PHYSICALLY STOP THEM. Allow them to search just make sure you dont say "ok, I guess, sure" or otherwise remain silent while they are searching.
Police can search all the common areas and your roommates room. Common areas such as kitchen, living room, family room, bathroom, garage, etc. Obviously having a probationer living with you does infringe upon your rights but that infringement is permissible.
The above information does not establish an attorney client relationship nor is it meant to provide legal advice.
Your rooommate can only give consent (which presumably is a condition of his probation) to search those areas that he exercises control over. That means the police can search the living room and kitchen, as well as his room. But if he has no right to enter your room, he can't consent to have the police search it. So you can object to them searching your room. The problem is, you object, they ignore you, then what? You could sue them, which would be expensive with little benefit since your actual damages (the loss of your privacy) are minimal. Or you could file a complaint with the Citizen's Review Board, which probably won't do anything. Thus, you may have a right which as a practical matter is unenforceable.
What Mr. Bogan says is 100% correct in theory. However I have had many drug cases where several people are living in several different locked rooms in the same house. If the police have a valid reason for searching one of the rooms and the common areas they often just search the whole house despite the signs you have hung on your door. This may make the intrusion subject to a motion to suppress if incriminating material is found but you still have the hassle of the search, getting busted and spending a day or two in jail. The only way to be 100% safe from this kind of intrusion is not to live with people on probation or parole, as unjust and cruel as that might sound.
Your roommate probably has what we call is a Fourth waiver, meaning his person or vehicle or residence can be searched with or without warning or reasonable cause. The police or probation officer should not search your belongings. They are not required to be neat, but, they should not trash the place. If you are present when they show up, tell them what is yours and what is his. Ask your roommate to do the same.
Any comments offered are not intended as legal advice. This attorney does not know the specifics of the particular case sufficiently to offer legal advice. You should hire a lawyer who can evaluate the details of your specific situation before offering advice.