Studio design help!

Hi everyone! Here is my story...... I'm looking to build a music studio in my (large-ish) garden. I would like to have a control room, a large main playing room to record a band (and rehearse) and maybe two very small rooms to record vocals and maybe amps in order to reduce leakage. I have roughly 25,000 euros (34000 us dollars) with which to build the basic structure. I'd like to build it underground, so as to reduce noise coming in (and out!) , and am wondering if there are any sort of ¨classic dimensions or shapes¨ for these sort of rooms. I am building the rooms from scratch so of course i can make them any shape i want. I guess I want to get it right now, and not have to change anything later. I'm also wondering if the walls need to be treated with anything special to avoid damp or if i need anything special in the roof of the place to avoid the same. The only neighbour i have is about 50 metres away. The area that would be for the control room is under the patio and is roughly 3.5 metres by 4.5 metres. maybe at a stretch 4 x 5 m. The main group playing room could be roughly 6-7m x 8-9 m. The vocal room and guitar room would have to be smallish, but as i can just dig more garden out for them, I was wondering if there are any ¨minimum dimentions or sizes¨ for those types of rooms too. obviously for depth, i can just dig down farther! I'm not that worried about acoustic treatment within the studio (Yet!, i'll do that bit by bit, buying foam etc), i'm just worried about getting the right dimentions to prevent standing waves etc. thanks in advance for any help!!