I'm going to write a book. ideas on topics to write about?

well depends what topic.. horror? romance?

here's some ideas:

the world ending
what will it be like in 50 years
a sad one.. maybe someone dies or something
someone trying to make it, like become famous in california or new york
a celebrity's point of view
realistic fiction.. maybe someone looses their job or something
a mermaid..lol
living in the white house
someone makes a wish that changes their life

ha well have fun

Sorry, but a true writer doesn't need someone else to give them ideas, they can draw ideas from absolutely everywhere. Look around you, what do you see? WHO do you see? What do you think their story is? Why are they acting the way they do?

If you're really and truly stuck for ideas, I'd recommend a story idea generator.
http://www.archetypewriting.com/muse/generators/plot.htm

Are your really sure you want to write a book? Considering how much "blood, sweat and tears," how much agony and effort MUST go into the writing of a book, do you really want to do it if you don't have a burning desire to communicate something?

Maybe this is not yet the time for you to write that book. Try writing some short stories and see how that goes.

Whatever you choose, good luck.

P.S. If you're really stuck for an idea, how about a modern version of some of your favorite fairy tales?