From what I've found online it appears the postponed possessive is used in some cases.
la mia casa would translate to "my house."
casa mia can be translated to "my home."
This is supposed to distinguish your home as unique.
I've read it can be a way to add more affection or meaning to the noun. Such use of grammar can also depend on regional usage as well.
"La mia casa è bianca" would have been ok, anyway. :)
If you have the possessive adjective followed by the noun, there must be an article before. There are some few exceptions, the bigger one is for relatives.
Mio fratello è alto.
La mia macchina è grigia.
Il mio amico è simpatico.
Mia cugina ha dieci anni.
Adding to Marziotta's answer, I had read in the earlier lesson thread that while talking about closed ones (fratello, sorella, zio, zia, etc.), if they come in plural, the article needs to appear.
For example: I miei genitori vanno alla porta (hope I didn't make a grammatical error here :) )