hiya and weclome to the forum - you will find people very helpful and knowledgeable!
TILES: It all depends on what style and condition, Cement tiles can get fairly brittle over the years I believe, so may not remove easily. What suburb are you in, as I am in touch with most demolition yards and may be able to advise
Also, what age is you home and do you have any pics for us to look at?
Finally, are you matching roof pitches etc on your garage and what type of door are you going to use?
Have fun!