So I know that "quam" can be used as an intensifier with adjectives and adverbs that expresses astonishment and things along those lines, like "Quam pulcherrima" and stuff like that.
But my question is, what if I want to do this with a noun? Like for example in English if someone sees a really nice looking building or something they might say "What a building", or if someone sees something negative, they might say something like "What a massacre"
How would I say that in Latin?
You can use the interrogative pronoun qui directly with a noun as an exclamation.
Cicero, Philippicae 8.1.24: An ego ab eo mandata acciperem qui senatus mandata contemneret? aut ei cum senatu quicquam commune iudicarem qui imperatorem populi Romani senatu prohibente obsideret? At quae mandata! qua adrogantia, quo stupore, quo spiritu!
Am I to receive commands from a man who despises the commands of the senate? Or am I to think that he has anything in common with the senate, who besieges a general of the Roman people in spite of the prohibition of the senate? But what commands they are! With what arrogance, with what stupidity, with what insolence are they conceived!
This usage is often paired with an expression of quantity, yielding basically "how great and how many":
Horace, Sermones 1.5: o qui conplexus et gaudia quanta fuerunt.
Oh what [great] embraces there were, and how many delights!
This usage is also found in indirect discourse:
Cicero, De Lege Agraria 2.26: Cognoscite nunc quae potestas x viris et quanta detur.
Now recognize what a [great] power and how much of it is given to the Ten Men.
Source: Oxford Latin Dictionary, s.v. qui, A, 2 and 3
You put it in the accusative, for example:
O mortalem malum! ("What a conniving personage!") Plautus
O corpusculum malacum! ("What a tender little body!") Plautus
O lepidum caput! ("What a delightful person!") Plautus
Bellum et pudicum uero prostibulum popli. ("What a sweet and chaste little street whore, indeed.") Plautus
Even if is only a single noun, the principle is still the same: it is placed into the accusative to make it exclamatory. For example:
iocularem audaciam! ("What a joke! What audacity!") Terence Phormio
These are all colloquial. In more literary Latin sometimes the nominative is used with or without supporting adverbs. For example:
Facinus indignum! ("What a shame!") Cicero, letter to Atticus.
O elegantia! O lepos! O venustas! O verba! O nitor! O argutiae! O kharites! Ο ἄσκησις! O omnia! ("What elegance! What wit! What beauty! What diction! What brilliance! What subtlety! What charm! What practised skill! What everything!") Fronto correspondence
Quale decus formae! ("What beauty of form!")
