I left the venision blind over the window so it looks like a normal window from outside. Then packed the window area with pillows, then a sheet of styrofoam
Whats your budget.
Old foam matresses are cheap/free big & quick. For jammin acoustics are not as important esp for drums.
Make sure the ceiling has insulation bats in it. The snare will smash it's way out through the roof otherwise
Bunnings sell acoustic insulation bats that work rather well. Cheaper option is fibreglass insulation bats, work great but make ya itchy as fuck.
Big blocks of foam are the easiest for absorbing sound, hence matresses.
Do some google searchin. Eltons book on acoustics is a killer book that explains it all in detail.
Best way is to build a room inside a room