In reply to French Erick:
> I am looking for what the title says.
Assume you mean
weight vest or belt?
If so, I've used both. I own a weight vest (XLR8 brand from NZ) with pockets so you can add/remove weight packets accumulating to a total of 10kg.
For actual climbing (especially so on a roof), I'd use a vest for better weight distribution. Unless of course you want to build exceptional core strength, then go for the belt. Although I expect a belt will hinder form too much unless you can comfortably do levers with additional weight at your mid section?
Another good one is to use mountain boots; not only are they heavy but foot placement becomes cumbersome, placing emphasis on core/upper body strength.