I'm not the one that mentioned this, and I've never tried heated roosts, but experience with electrical work makes me think that heated roosts could end badly if you are not very careful making them. I assume you would use heat tape, like for wrapping pipes. They are not made to be picked at by peafowl, so you must cover them with carpet or something to prevent access. Carpet insulates and holding the heat in both reduces the effectiveness (so you might need more tape per linear foot) and increases the danger of fire. If you don't cover them you might also get hot spots and that could burn their feet very easily. Birds have poor pain reception in their feet, we have a turkey hen that let a rat gnaw her leg off one night while trying to incubate eggs, I could easily see a pea getting a severe burn and not realizing it, so it's up to you to make sure that can't happen, they have no experience sleeping on branches that are hot enough to burn them.I don't want to "steal" this thread, but the heated roosts post really disturbed me as its one of the easier ways to help peas out during really cold weather. Can you tell us more about how the peas were injured by it. I hadn't heard of this problem before.
I'm not saying you would build one badly and burn your coop/shed/barn down, but I would recommend caution. There is no UL rating for heated roosts, nor are they covered by any electrical codes, so you are on your own as far as design and building.