Help with my new square recording room

Hello! I've been reading and reading all the topics the past few weeks and I can say I'm now more confused :) I have a small mixing studio in Greece with a control room and a small vocal booth. I have a room available next to my control room which I'm planning to convert to a recording room. The problem is that the room is almost perfectly square and it has a large window on one side. The walls are brick with a concrete floor and ceiling but one of the walls is not build yet. I am planning to construct a room within the room with gypsum boards and have a window to have visual contact with the control room. I am not interested on really good soundproof since I am on a location with no neighbours nearby and I can go loud with no problem at all, all i want is good separation from the control room. My main goal is to have a room where I can easily record a drum set or a small band playing together. I already have the booth which is pretty dead so I want my new room to be rather lively! The dimensions of the room are 4.80m x 4.70m x 3.10m height. Do I have any chance with the square room or should I drop my plans? :( I'm including a layout of the space and a layout of the front wall which already has an aluminium window with double glass. I'm planning to include a second window from the inside. I tried my best to include all info, I hope I haven't missed anything! Thank you for your precious time!

welcome! the large room which is almost square shouldn't be a problem because you can change some of the wall angles and corners with full size slat resonators which will work nicely. it's not a critical listening room so asymmetry will help and using hard treatments will keep it lively for the drums. you could readily add some porous absorbers to finalize the room response. on the ceiling you can use polys to break it up. make the poly panels hang a bit and angle slightly. put some patchwork of absorption on the ceiling above them. this will make a nice live diffusive ceiling.