I would not use "preserving of historic buildings". It is technically possible to use "preserving" as a noun, but "preservation" is I think much more common. I looked at the Google Ngram Viewer and Corpus of Contemporary American English (COCA), and the results supported this. In COCA, "preserving of" was pretty rare, and a number of the examples that I looked at were in contexts where coordination seems to have provided an extra reason to use an "-ing" noun (e.g. "the writing down, cataloguing, and preserving of ski history", "the restoring and preserving of wetlands" and "the protecting and preserving of Christianity").
The issue isn't so much that "preserving" would have a different meaning. Rather, I think it's a matter of something called "blocking": the existence of the noun preservation kind of "fills the space" that could otherwise be comfortably occupied by a noun preserving. If you use preserving, people might wonder why you didn't use the more common noun preservation.
The use of "of" in your sentence means that preserving is not a "gerund" as that term is commonly used in modern grammatical descriptions of English. Typically, the word "gerund" is reserved for a verb form. A gerund would take a direct object without the preposition "of". Preserving would be a gerund in a sentence like "Preserving historic buildings is important."