Thanks Chaps for the warm welcome to the forum.
Gérard, I did build several loudspeaker enclosures for myself. You will save quite a few bucks building your own boxes plus the satisfaction of doing it yourself. The great majority of loudspeakers and audio equipment for that matter are tremendously overpriced, I would say a ripoff, some costing up to £5M, no typo, but nothing will sound like a real live concert no matter how expensive.
You will find the excellent monitor Focal Aria 5 kit, since it is made in France it will be much cheaper than here in the States, there are several French manufacturers such as Audax or JMB that sell kits. I bought kits in the UK at Falcon Acoustics and Wilmslow Audio, they both have websites. Use 3/4" MDF or 3/4" Baltic plywood, it is better than regular plywood.
Horacio