@sachinee- Yes, and lead is highly toxic. But I think nomii means graphene which is not actually quite the same thing as graphite which is what we use in pencils today.
Graphene is 200 times stronger than steel and is very lightweight and thin. It can be made only an atom thick and maintain quite a lot of strength. The issue with using graphene in materials right now is price. But even if price is taken care of, using graphene in buildings has an interesting problem. Pure graphene is very brittle. When i tbreaks, it shatters like glass. So you could build a strong building out of it, but if a force broke the graphene, the whole building would crumble.
We need to essentially create graphene alloys to make it work which is a whole new level of material science. You need something which bends and flexes under pressure but also has the strength. This, by the way, is one of the reasons why we invented steel over iron. Most early iron methods made very brittle objects, too.