I'll do my best. Let's take it one sentence at a time.
1. As you know, next month will be Peterís birthday, so we are looking for a present for him.
That one is perfectly fine. Good start!
2. I am discussing with some friends of us about what is the best present for him.
Too many words! Try:
- I am discussing with some friends what would be the best present for him.
3. Some of us suggested buying some clothes, I agree with them and I hope you to.
That would be better as two sentences. Try:
- Some of us suggested buying him some clothes. I agree with them and I hope you do too.
4. Now we must choice the present.
You need to use choose instead of choice there. Choose is the verb, and choice is the noun.
5. A trousers is a good alternative because he is always wearing the same trousers and I think that it would be useful for him.
You can't use alternative there, because it doesn't mean the same thing as choice.
- I think it would be a good idea to get him a pair of pants, because he is always wearing the same pair of pants.
You can use trousers instead of pants. (The first is BE; the second is AE.)
6. Another possibility, are some t-shirt because he prefers wearing t-shirt instead of shirt, but the problem is that we do not know what kind of t-shirt he likes.
- We could get him a T-shirt. I know he likes to likes to wear tee-shirts. The problem is that we do not know what kind of t-shirt he likes.
By "kind" are you referrring to design? Whether it has printing on it or not? Color?
7. Other friends proposed some sportís article like a tennisís racquet because he had broken his racquets two months ago.
- A couple of people suggested getting him a sports article, like a tennis racquet. Since he broke his racquets two months ago, he might appreciate that.
8. So, either the clothes like t-shirt or trousers or else the tennisís racquets are the best alternatives to give him as a present.
- We have decided to get him a T-shirt, a pair of pants (trousers) or a tennis racquet.
9. I hope that you could contact with me as soon as possible because we must decide what to buy until next months.
Please contact me as soon as possible, because we must decide what to get him by next month.
PS: Do not said anything to Peter!!!!.
PS: Do not say anything to Peter.
What do you think?