Takeing acoustical measurements

Not sure if this is the right forum so feel free to move it but I figure measurement is the first step in the design and building process. I have searched the forums but I cant seem to find exactly what im looking for. So if the info is on here somewhere im sorry for bringing it up again. So my question has to do with with taking acoustical measurements of anything besides a control room which I feel has been prwtty well covered everywhere. what im wondering about is stuff like placement of the measurement mic, placement of the sound source. I assume its a good idea to have multiple placements throughout the room but where is the best starting point and what is the ultimate goal? For instance in the control room your trying to achieve the flatest response and equal decay times in ONE spot. But in a larger room your looking for this every where. Ive also heard of people poping baloons to see the early reflections. Again the position of the source and mic are what im wondering about. I dont want make this to long winded but the other part of this question is about placement of instruments in the room and how you can use the measurements to design the room so that for instance this portion of the room is designed to make the drums sound theyre best. Is this something that really goes on or is a room designed to just be the same throughout and if so what method of testing is used to try and come up with best result? Thanks in advance for any insight you guys can offer.