OP, for an 8x3 setup, you're going to have to use multiple lights to cover the whole area. If you use HID lighting, I think you'll need two 600-watters. If you go for LED lighting, I'm not sure what you'd need. I'm just now getting into LEDs myself.
My situation is very LED-friendly. I'm a small, personal grower. I have a small 4x4 grow closet. And now that I've learned to SCROG, it's probably all I'll ever do. So my situation is perfect for LEDs. Small grow area inside my house, eliminates my heat problems in the hot summer (i.e. allows me an extra grow per year), and SCROG eliminates light penetration problems since all my buds are at the same height.
In your case, just starting out, and having an oblong (8 x 3) grow area, I'm not sure that LEDs would be the best route to go. HID is gonna cost less up front, and you can even find good used reflectors on Craigs List. I might even try a used ballast for my first grow or two. But make sure to change bulbs at least once per year. Start small, and give it time to make sure you're gonna like growing before you set up such a large area with top-of-the-line equipment.
I guess I'd like to ask why you want to start out with such a big grow area?. New growers make mistakes and many times fail on their first grow or two. I'd suggest starting out with a nice, manageable 3x3 or 4x4 grow room. You could even buy a tent of those specific sizes. Tents are good for beginners because they have so many problems already solved for you. Reflective walls, air intake and exhaust vents, supports for hanging heavy equipment, and they're very portable.
And for my first grow or two, I wouldn't try SCROG. You have many things to learn about basic growing, so I'd wait till I had a few grows under my belt before adding the extra work of SCROG.
Expert growers, please chime in here to correct any bad advice I may have given the OP.