It is so sweet that you are trying to take care of a bird that is homeless. Most birds will make or find a way to make a nest. You didn't mention if this bird was just a baby and couldn't fly or if the bird was injured. If it is a baby bird, and if it's mother doesn't come for the bird, then I am afraid the bird is doomed, to the elements of the weather and lack of food and if you handle a baby bird, then the mother will more than likely disown the bird and it wil die. If you can get the bird to a humane society or a vet, they may be able to care for the bird. If the bird is older, I think an outdoor birdhouse and maybe stuffed with straw or hay would work. I wish I had better news, but thanks sweetie for your kindness