[font=arial, helvetica, sans-serif]Good Soundproofing is a good start, we really like a room that has good acoustics, you can rehearse at a lower volume and hear every instrument, if a room is boomy it tends to mess the frequencies up, IME.[/font]
[font=arial, helvetica, sans-serif]Adequate Ventilation is a good one, too many memories of being stuck in a sweatbox room with no air and 4 sweaty blokes![/font]
[font=arial, helvetica, sans-serif]controllable lighting to enhance the creative atmosphere, we had a rehearsal room with coloured lightbulbs and a dimmer switch, much better than a couple of strip lights.[/font]
[font=arial, helvetica, sans-serif]with a bit of thought and some canny ebay purchases this is possible to do quite cheaply.[/font]
[font=arial, helvetica, sans-serif]good luck with the project and to a great rehearsal facility,[/font]