a studio inside of a cob house

Hello, I'm about to build a house were I plan to have a studio. It's mostly for playing (I play piano and a cello) but I wish it could also be used for amateur recording. The house will be built from cob (a mix of clay, sand and straw) so also any shape of room is available, not just rectangular forms. The size of the room has to be not too big - 70 to 100 cubic meters, so here is a question: are there any solution that could optimize the acoustics by building curve walls, ceilings in different levels etc so that it would help to minimize cost for futher reconditioning like adding traps or diffusors. I'm in Ukraine and we here do not have a big choice of material. Ideally I would like to have a decision witch gives perfect acoustics only by the room shape. Also the material allows to have cavities in the walls, I heard this was used in churches. I don't care much about the noise, as I'm far apart from the neighbours. The entire purpose is just to have a reasonably good room for playing acoustic instruments. I will not be able to invest much in expensive materials and it is preferably for me to have natural material like wood of straw everywhere. My budget for room reconditioning is up to $1000, the less - the better.

Acoustically, bales of straw placed in corners should help sound quite a bit, if you don't mind taking the chance on being INCINERATED when some dufus decides it's OK to smoke in there :!: :!: Aside from that, build no walls parallel to another wall (same with the ceiling) - 1 foot in 10 (.3meters in 3 meters) splay between opposing surfaces will solve flutter echo problems. Pick ratios of length, width, height that are NOT even multiples of each other - 3x5x7 meters would give a VERY smooth room response (105 cubic meters). These numbers should be the AVERAGE distance between walls, not minimum or maximum. You would likely STILL need to lower the reverb time though; to do this evenly, it takes quite a bit of thought/planning, and likely searching for sources of materials. It's also possible, given your particular instruments and depending on musical style, that a longer reverb time may suit you just fine... Steve