This is a tricky one. If she likes you, a simple "Hey would you like to do ___?" would do. Or perhaps some other expression of interest, it can vary. However, there is a line. Never, under any circumstances, tell an unrelated woman that love her without ever dating her. "Hey, I've known you for a while, and I love you." is like woman repellent. It almost never works, and now you're most likely going to be labeled as creepy. Also, anything that would sound more clingy than that, such as an unironic love letter, a traditional Mariachi band under her window, or 20 roses. Good luck.
Telling a female how you feel.