In reply to FreshSlate: My recommendation would be essentially identical to TRip's.
If I was trying to onsight 25m lead routes indoors (as opposed to redpointing the entire time) then I'd be very happy to use a 9.5mm rope for that, so I can't see the maximum height of your local wall, in of itself, as ruling out the option of a shorter rope.
The bigger issue is that choice of ropes in the range 30m-40m is depressingly limited. Various budget 10mm ropes are available but it is much harder to find something good value around 9.8mm with a basic dry treatment.