I need to know how to say this in Spanish?

Es tu decision, A mi no me importa lo que tu decidas.

you r welcome =)

I would definitely go for chemMan's version if u r politely telling someone they can choose, whatever their choice u don't mind (like in, someone asks you where u'd like to sit during a flight, window or aisle, and u tell the other passenger he can choose).

If u want to tell someone (on a somewhat angry note) they can f.ing do as they please - u don't give a s..t (example: a two-timing boyfriend who can't make up his mind), i would definitely go for Skyhigh's version (definitely colourful, it would really work in such a context..)

Es tu opcion. Me da igual de cualquier manera.

Es su elección. Yo no tengo inconveniente en de cualquier manera

Es tu decisión. No me importaría de cualquier forma.

Es tu decisión. De cualquier forma, no me importaría.

Es tu problema. A mí no me importa un carajo.

(It's a little more colorful than the other answers, and yes, it's technically correct, but use it only with close friends!)

Es tu decisión. No me importará, cualquiera que sea.

Something like that.

Es decisión tuya. No me importará ( or me dará igual) sea lo que sea.:)

es tu decision. no me importa es mas

como tu quieras. a mi no me molesta.

;-)

I think this is easier