[zuminator]

There is a formulaic way to transliterate words based either on their roman lettering or their pronunciation in their native tongue. But loanwords aren't always mere transliterations, they often have some kind of adaptation or simplification. So like for example the word building would be nigh impossible to transliterate relying on its roman lettering alone. It would have to be pronounced something like buierujingu. Using its pronunciation in English would be a better starting point; transcribing that into Japanese sounds would be like birujingu. And what Japanese actually does is take birujingu and cut it in half, and thus the actual word for building is biru. (Well, not exactly. Biru is just talking about modern buildings, like concrete and/or steel construction. The word for "building" in general is tatemono.)