I wouldn't build something without knowing that it will be great.
As I said in the "Diy Monitors - to build or not to build" thread, you should build this project: http://www.geocities.com/diyproac25/ because it is a clone of a very good sounding and expensive speaker, but if you build it yourself it will be relatively cheap.
It uses ScanSpeak speakers that you can buy from Madisound.
If you want to build them you should do them exactly like in their description. A loudspeaker is an optimised system, so any modification will make it worse.
If you can't afford the space build some minimonitors.
Although I think this Proac clone is at the same time a great tool in studio or for listening music at home. And don't forget, it is not very expensive.
There are very few DIY speaker projects where you can be sure that they will sound great. This is one of the few.