Gender

I work with two girls who are pregnant. One found out gender at 10 weeks and one found out at 20. I'm having twins and judging by my friends who go to the same obgyn they aren't going to tell me til I'm 20 weeks. I want to know sooner so I can start planning and doing some construction on the rooms while I'm still feeling ok. I'm thinking of going to a special place for an ultrasound who do gender at 14 weeks. Do you think my obgyn will be pissed and what are your thoughts ???