The Idea is pretty usefull:
Parking spots in the city can be bought by the player.
Several times when I had to do a manual delivery or just go back home, all the parking spots are taken.
If you buy it, it will always stay free of NPC cars.
Some can be more expensive than others depending on the road and place.
It will be good also to have vehicle warehouses or maybe a spot for big appartments.
a garage for appartment would be nice tho
like an underground parking like in the real NY city
That actually does exist right now. There are a handful of underground parking lots in the game where you can drive down and park your car. You still have to pay hourly, but they do exist!
I know this is going to be an annoying answer but I’ve been buying warehouses to use for parking. I would like to have an apartment with a parking spot but I would also hate having to have an extra screen to go to (Apartment > Garage > Street instead of Apartment > Street). I’m down for a parking lot or something though.
Interesting idea! 
But you just avoid the actual parking spots and park them randomly inside?
I have an apartment across the street from one warehouse so I just go across the street and park depending on what I am doing. I just bought another for my sports cars, but I still park some other cars out front in the parking spaces if I’m in a hurry.