You can build real estate gradually, starting with one, two, three apartments paid for with your job and rent your tenants pay. At some point, pretty early you could stop working but if you don't you can buy additional apartments faster. During first generation, I think, you could buy around 10 if you have a good job. Your children will be able buy faster, their grandchildren even faster.
A friend of mine from college had parents that started from scratch and bought and rented ~1200 homes in Indiana during their working years. So, it can be done.