The first thing one has to learn, is compromise.   A character that may have suited your tabletop game for the last ten years, may not fit in with the room you want to put them into, even if its almost nearly the same campaign.  The rules will most certainly be different, and there may be a restriction on certain aspects of character creation in the interest of fairness, and diversity within the room.  For example, a room may have a certain quota already met for magic users, so you may have to adjust WHAT KIND of magic your character uses. Or perhaps your character is a telepath, and the room you seek to play in, has severe restrictions on telepathy.   It can happen.  It does happen.

Instead of getting angry, and giving up. Consider giving your character other abilities that may or may not be related to your first choice.  Or bring them in currently unpowered, until such time the quota is lifted, or there is an opening for that type of character, perhaps they can develop these abilities over time.

This section will give you a heads up, on how to build a character, from the initial concept, to finished, and fully fleshed out.