1. to add buildings to an area of land or a neighborhood.
> They are really building this area up. There is no more open space.

2. to develop, accumulate, or increase something, such as wealth, business, goodwill, etc.
> I built this business up through hard work and hope.

3. to praise or exalt something; to exaggerate the virtues of something.
> The master of ceremonies built the act up so much that everyone was disappointed when they saw it.