Item Build Calculator / Testing

Does anyone know where I can find an up to date online item build calculator? One that allows you to assemble item builds and see actual game stats update in real-time?

I don't count guide/build sites like MobaFire that show you build paths, but don't let you actively swap or change items to effect stats.

LeagueCraft has one but it is seriously out of date, both in items and champions. http://leaguecraft.com/builder

What I'm trying to do is be able to experiment with different builds quickly to find what is the most powerful/cost effective build for certain situations.