if this is an accomplished carpenter than there are only a couple of measurements that they will need to get the job done. canopies are just four sided boxes. they can be simple or complex. all you need to do is find a set of plans that you like and tell the capenter that you need it with these inside dimensions. 60"X18"X12" tall. it can easily go taller if you think it will look good, but most people prefer shorter canopies. if you can get the carpenter to make the entire front of the canopy hinge upwards and lock that would be very helpfull. if not than have panels on the front that can either be removed or hinged upward so that you can do maintenance on the tank.
here are some pictures of my canopy. this is a double hinged type. a little more complicated to build. may not be totally suitable for what you want because the reflectors shown below are wider than mine so they would get in the way when you do maintenance. these are old pictures. i also added three 4" fans on the top of the canopy to help in ventilation. fans will be a must if you are planning on using 400w MH's.
here is a link to what you need for the sockets. you need a reflector. these will need to be centered over the holes in the acrylic top for best light dispersion.
some people also prefer to have
VHO lights in the canopy also. in the pics above you will see mine. not totally necessary since you have 400w MH's but they do help in ramping up the corals for the day, and they also help in correcting colour shifts, so it is more pleasing to your eyes.
a nightlight can be added whenever you want. they are usually just peel and stick items.
i know i did not help you out as much as you wanted, but it is difficult to give exact plans to someone since every tank is different. the best thing to do is find a carpenter friend who can come over and look at all the stuff you want to put in the canopy. then discuss ideas from their.
BTW-the ballasts will not go in the canopy, just the reflectors and the sockets. the ballast will go below in the stand.
G~
