Most aftermarket lightbars use 20w or 35w halogen bulbs. The main trick is that the stator on the bike is only rated for an additional 70w of load. So if you have any other add-ons that use power, you have to add up all the watts to see what you can stand. I unfortunately added 140w a couple years back and toasted my stator over about a year. Just because the lights work does not mean that you are not overheating your stator and in the long run will probably have to replace it if you add to much load.
As for building one, I can't really help much there. I did the Wally World lightbar thing at one time. But that is just a matter of clamping a couple lights to the little chrome bar that runs under the headlamp on the Classic. In your case, you may be able to make a couple brackets that attach where the turn signals are located.
'07 VN900 Classic
Horsepower is an illusion.
Torque is the source of all good things.