You can use two forms, you can either say "¿Qué hay si es que...?" or "¿Qué te parece si?" (The latter version is actually "what do you think if?") Of course the main difference is that in the first one you are presenting a potential scenario and you want to know the possible consequences, whereas in the second one you are asking what the other person thinks about that scenario. In practice they can both be used to ask someone's point of view. Examples: ¿Qué hay si vamos al cine mañana en vez de hoy? = what if we go to the movie theatre tomorrow instead of today? ¿Qué te parece si vamos mañana al cine? = What do you think if we go to the movie theatre tomorrow? ¿Qué hay si tu vienes hoy y yo voy mañana? = What if you come today and I go tomorrow? ¿Qué te parece si tú vienes hoy y yo voy mañana? = What do you think if you come today and I go tomorrow? I hope this helps.