if I had an awful lot of money, I'd first buy some realty for myself (not quite expensive, definitely not luxurious, a good apartment in the city and a good house in the removed suburbs would suffice), and did a health checkup, then fix what can be fixed (I have a lot of health problems but they mostly aren't fixable)
next I'd do the same to my relatives and old friends, also pay for their kids' education, my nieces and nephews included (my own kids probably won't exist, not because I can't but simply because no sane woman would want them from me)
and then I'd try and fund people working on stuff I'm interested in, covering the most pressing expenses for them — housing, health, and education

buying out realty just so nobody else could use it, or merely for speculation, seems pretty stupid, guess I'd find something better to do with the money
but even having a billion (of no matter what currency) I'd definitely come for another one, just because it's better be me who decides what to spend the money on than the stupid and corrupt politicians