How tall should your grow room be?

I have a space that is only 4.5 to 5 foot tall...is that enough space for a DWC grow?

Sure, why not? My plants never get more than 3 feet tall, and I could keep them shorter if I wanted to, by more topping or LST. You'll need some room for a light and fan, but if you use fluorescents or a cool tube, you can have the lights practically on the plants. You could also use an Emily's Garden - type setup, which works great, and the net pots sit right on the bottom of the reservoir, like in my LSTTT thread.

You could also grow Lowryder or some other autoflower strain.