If someone told you to build a church, what would you do? You'd probably contact an architect and describe to them your vision for a nice building. Steeple or no? Modern or traditional? What about ceilings? Windows?
In Matthew 16:18, Jesus says, "Now I say to you that you are Peter, and upon this rock I will build my church, and all the powers of hell will not conquer it."
Jesus says that he is going to build his church, but he makes no mention of blueprints, hammers, nails, windows, doors, or wood frames. None of this, yet the church will stand. And not only will it stand, but the supernatural powers of hell won't be able to destroy it.
If somebody asks you to describe the word "church," please do not use any sort of physical structure in your definition.