...right...  take it up with judge Judy. 

"What should I do?"

You should make an archinect post about it!

But seriously, is your professor using "your design" for a competition or for a client proposal? Tried talking to your prof about it or contacting them via email? Before taking any further steps, if at all, try taking it up with them first. 

Maybe they could hire you in the office to develop your own concept further ;-)

What was the copied work used for? Was it built, a competition entry, what?

be happy that someone with the resources to win work and execute it took a shine to a concept you helped develop and implemented it. 

Ideas are cheap. The cheapest actually. Execution is the hard part.

In this profession, the more you can let go of "your ideas" and embrace "ideas" or just "architectural ideas" in the generic, the better you will take and give criticism, and the better your projects will become.

(edit: i'm writing from the assumption that he took some concept-level student work and applied it to a built project. Which i'm 100% ok with. If this professor took a speculative proposal or student work and repackaged it as his own speculative proposal or research, not ok with that.)

Nothing much can be done except burning a few bridges through social media. This happens in grad school/phd programs often.

Honestly those ideas are probably a lot less yours than you think. A lot of professors use studio time to explore things they have been thinking over and plan to later use in their own work. Be happy you got to work with him, and learn what you can from it. 

an important key to survival in architecture is to practice non-attachment to ideas - don't be some Howard Roark

Technically those ideas probably aren't even yours: courts usually find that academic work, and the right to any profit or publicity to be gotten from it, belongs to the university.  Usually you've signed something to that effect in your admissions or registrar's fine print (or something agreeing to abide by the student handbook, which in turn contains that fine print.)  

Even if you presciently take steps to formally copyright your student work, good luck preventing professors or guest critics from appropriating cool ideas - google Shine v. Childs and Freedom Tower for an example that got a lot of press, dragged on for years, but eventually fizzled out without deciding anything new about ownership of architecture students' ideas.  

Some profs regularly make their current professional projects into the topics of their studios: constant supply of fresh schematic design ideas.  You should suspect this whenever you encounter a project with a program that is particularly specific, especially if the site is fairly local (example: new performing arts center for a particular private high school nearby, at which the director just happens to be an acquaintance of your professor, and is able to give your studio a personal tour of the campus, and later shows up as a guest critic at the final review.

nothings original, get used to it

What country?  In the US and elsewhere, he could get into serious trouble for Plagiarism in the educational realms for not crediting you.  First step if you want to escalate is talking to the University to whomever in administration looks into this stuff.  Also be prepared that they may push back your work was influenced by their reviews.  If you have verbatim sections, then it's pretty hard to say he didn't copy your work without permission or give you credit for your contributions.   

I don’t know how to reply to a specific comment so I will write here.

He used that in his own office’s research and it will be presented on an important event.

And we are not attached to the ideas. The thing is, the design is 90% similar to ours.

Moreover, he told me he “want to do something relevant to our project but will be very different”. At least, shouldn’t he mention that his research is based on our studio?

I know it is a common practice but does common mean “right” and “legal” ?

This is a serious problem in architecture field. why should we keep silent And try to get used to it? 

You said the project will be presented at an event.  If it hasn't happened yet then how do you know he's not going to credit you in that presentation?  If you want to push him toward doing so, why don't you just speak with him or send an email to say "we would appreciate a mention."  Copy your department chair or Dean or whoever is in charge of your department, so the professor is aware it's on multiple radars.

A big issue is that you say the design idea is "90% similar" and that he did not change "many" of your words.  The threshold for design copyright infringement is pretty high: a design that's different in 10% of aspects, or even 5% or 2% is likely to be judged to be a different design.  With things like architectural plans and elevations, just flipping/mirroring them from right to left or changing window types have been changes that courts have considered enough to constitute an entirely different design.  There's also the issue noted earlier that you may not have standing to pursue this in court if your university is the owner of the intellectual property instead of you. 

With plagiarism there are a lot of different tests - the most simplified is that there be multiple strings of 8 or more consecutive words that are completely identical.  If your prof kept "many" of your words, but not all, then it may not fail that test, so then it goes to less simple tests about the overall meaning of the text, and about how common the phrases are and how likely they would coincidentally occur in this context in different peoples' writings. 

I don't think most are saying that you shouldn't push back on this.  You probably should.  But if you're looking for a satisfying resolution within your institution, you've said yourself this is a person with some power, so report it and maybe your university will take serious action, but maybe not, so just don't be too surprised if it ends in a hand-slapping at best. 

If you're looking for a legal resolution then shop it to some intellectual property lawyers and see what they say.  First consultations are usually free, and you can call a few and at least get a sense of the relative chances or futility. You can also see if you can get a legal clinic to take it on pro bono.  But if anybody thinks that you do have a viable case, consider how deeply important this issue truly is to you (or not), as you could be wrapped up in a lawsuit for years after you graduate, still eventually lose, and sometimes the loser ends up on the hook for the other guy's legal costs.  I'm not saying don't pursue it, just know what you're getting into.

Depending on the institution- go to the ombudsperson, and then go to the provost along with all the other people the ombudsperson suggests you contact. Word of caution, the Ombudsperson might not have any clear course of direction for you, but it's a big step in creating a clear paper trail for your complaint. 

we should see pictures of both designs to judge if similar or not. 

update：

He replied our email and agreed to credit us.