i am building a lego model what is the best glue for plastics
I would go to a store that sells model cars and ask them. Michael's and similar stores have aisles of glues and there's probably one that will say you can use this on Legos or something less specific like use this on plastic. I'd probably just try Crazy Glue and see what happens with that.
Legos are made of stryene and glue suprisingly well with styrene(plastic model) glue. If you want tube type use Testors red tube glue. You can also use a liquid type such as Tenax, Ambroid or Weld-on. This will yeild better results applied with a brush or a needle bottle. Basically you're melting two sides to weld them together. You have to be careful not to run this down any exposed faces as it will mar the surface. Also make sure you have adequate ventilation. Both types can be found at a good hobby store.