Go to rosstraining.com for instructions on how to build useful workout equipment.
Anyways the equipment you buy should be a reflection of you goals. If you want to get big and strong you should buy a squat cage, barbell and weights. If you want to become explosive you should buy a barbell and bumper plates for the o-lifts (maybe some other random stuff for plyometrics such as vertical jumps etc), if you want to look like a gymnast you should buy some adjustable rings and parralel bars, if you want "functional strength" or whatever a medicine ball, sandbag, tractor tire and hammer might be of interest. Likewise I would use kettlebells more as a conditioning tool (a fun tool at that) than a strength tool. I don't think dumbbells are as versatile as barbells unless you're in a wheelchair (you won't be able to load properly for leg and lower back exercises).