THis question mimics a similar question about mathematics - is it discovered or created.
Our Rabbis ruled a lot of Halochos. Some of them are considered "the revelation of the original Halochos G-d gave to Moses", for example, what the Gemmorah (Temurah 16a) says :
במתניתין תנא אלף ושבע מאות קלין וחמורין וגזירות שוות ודקדוקי סופרים נשתכחו בימי אבלו של משה,
אמר רבי אבהו אעפ"כ החזירן עתניאל בן קנז מתוך פלפולו
A different type of Halochos is what the Rabbis ruled by their authority to rule. A good example would be everything that the Rabbis Paskened knowingly against the true Halacha, as in the cases of Tanuro Shel Achnai or that money does not buy in place of Meshicha.
My problem in studying the Talmud is the amount of effort I put into understanding the veracity of a particular ruling: if a Halachah is revealed it should reflect some kind of divine truth, while if it is simply ruled or accepted, it is pretty arbitrary, and there's no way of attesting its veracity.
For example, a Succah's height can't be more than 20 Amas or should be at least 7 Tfochim wide. Is that how G-d sees what a Succah IS, or He didn't care and authorized the Rabbis to come up with whatever their imagination tells them, in a sort of "החדש הזה לכם" - you decide when you want your months to begin.
For all other cases, where it does not say "Halocho Lemoshe MiSinai", is there a way of knowing that what the Rabbis ruled is "Heavenly truth" or a "Rabbinical decree"?
(Needless to say, it has little of a practical difference, as both have the same power.)