What proper words should I use in the following:
1) A teacher tells his students
I am going to take a glass of water. Keep quiet, I should not hear any noise
this is the part of the sentence where I don't know which proper words to use
2) Should I use costly or costy in the following:
Gold is a costy/costly metal.
3) If some one want to go up to the roof of the house what should he say
I want to climb the roof
or something else.