Jack of All Trades by Rain Carrington

Jack Pengrove lives a secret life in a magical city. He was born to a powerful family of witches, but he, unlike everyone else in his family, never acquired powers.
Leaving them and their horrible treatment of him for his lack of powers, he moved to Valleywood, hoping that being surrounded by magical beings would help his familial gifts finally come to him. Already there for years, however, he has little hope left.
Doing jobs through a temp agency that covers for the prostitution ring it truly was, Jace makes enough money to get by, but still dreams of more.
After the huge blizzard that buries Valleywood, Jack gets a straight job, fixing a roof for a man who collects classic cars.

Maltin Graves is a half-witch. With his powers being finite, the man who has lived nearly two hundred years knows that every time he uses his powers, his life shortens.
Graves’s warehouse houses these cars and also the man, in a beautiful loft above the cars, where he can always watch over them. He’s a writer of screenplays for the major studios in town, and that leaves him to live almost as a hermit. Rarely going out, he has everything he needs in that warehouse.
The two clash instantly, and Jack finds his new employer not only rude but also aloof. So why, then, is he so drawn to the guy?
Could it be they are fated mates, and if so, what kind of shifter could they possibly be? The terrible dreams that begin for Jack could hold a clue, and one that makes him fear himself more than he’s ever feared anything.