Is it a good idea to give our GM ideas/puzzles/riddles for his campaign?
If it is, how do I bring up my idea without offending our GM?
I don't want him to think that I don't like his campaign or anything of that nature.
Yes. The more the dungeon master know about his/her players the better content he can make for you to play.
If you present an idea with specific examples he would not be able to use the specific ideas, because you would know the answers ahead.
Start by presenting this idea in general, and if puzzles are unfamiliar to him, give him some links from the Internet to study, that way you wont know what's coming.
A group where the players and the DM can communicate about what is interesting is necessary, to keep the story alive. (I have been playing on the same story for 3 years now) and that is because he listens to our wishes, ideas and advice. (That does not mean I always get what I want, and I have to fight for it and have good arguments ready)
Make a forum where you can communicate about these things, it pays off.
To have a group that continues to come back for more, you need the same acknowledgement as you do in school,at work, within family and among friends, to be heard and respected. That goes both for players and for Dungeon Masters
If you love to play in the world he created, it will unavoidably lead to you making changes within it anyway, and puzzles are just one small part that could be interesting to influence. City names, invention of NPC's you are not related to from the beginning, just to make a few examples.
He should take that as a huge compliment.
If you are afraid of his reaction, make the forum online somewhere, and post the topics there, for only your group to read. It will give him time to think about things properly, before answering, and none of you will feel overrun by the other part.
Personally, as I a DM I would love this kind of interaction with my players.
That being said, I do think it is a great idea to suggest things that you, and maybe the other players, would find fun and engaging.
Make sure to not belittle anything they have done in the past, as then they will think that you have just been gritting your teeth to get through their content.
I wouldn't go into specific details about the ideas/puzzles either, if anything your suggestions should just serve as inspiration for your DM.
Eventually, if you continue to give suggestions, the DM will be able to use your ideas to seed future content that is well tailored to your group.
Depends on your GM. Some are control freaks who take up the GM seat because doing everything appeals to them. Some are lazy (in a good way) and would love it if the players took on some of the burden of the game.
This is really more of a social interaction question than an RPG one. I'd straight up ask the GM what you asked us and take it from there. There's a chance that will offend him, but if it does I'd wager something else would offend him later down the road.
I've never tried doing that, because my DMs are better at coming up with ideas than I am, but yes, I think it's a good idea. Just make sure not to be too specific - what you need is not to give the DM specific things, but give him ideas they can build their own ideas upon.