Is this a good way to ask a girl out?

well, i've been good friends with this girl in my year for some time now, since y7 and am currently in y11. i did ask her out about 3 years ago now but at a really crap time. I really like her and just want everything to go perfect but also make her want to go out wih me. she is not the shy type really, but is when shes around her friends. i was thinking of maybe buying a rose and making a sign that said, "do you want to go out sometime?" then going outside her house and calling her telling her to look outside. but i don't know if thats a good idea or not and don't want to ruin our relationship or anything. please help