Formal:
* Gostaria de ser seu amigo/sua amiga. (I would like to be your friend)
* Quero ser seu amigo/sua amiga. (I want to be your friend)
Informal:
* Quero ser seu amigo/sua amiga. (I want to be your friend)
* Vamos ser amigos/amigas? (Let's be friends?)
* Que tal sermos amigos/amigas? (What about being friends?)
Other options:
* Seria legal sermos amigos/amigas. (It would be cool to be friends)
* Acho que a gente pode ser amigos/amigas. (I think we can be friends)
Important:
* Amigo/amiga is the most common word for "friend" in Portuguese.
* The gender of the person you are talking to will determine the correct form of "amigo/amiga".
* "Seu" and "sua" are possessive adjectives meaning "your". Use "seu" for a male friend and "sua" for a female friend.
Remember to adjust your language based on the situation and your relationship with the person you are talking to.