Site location; the net acres suitable for building, site shape, and topography.
Prior zoning: can the site be rezoned for church use?
Environmental factor: Was the site ever a dump or an old factory?
Verify that the site has all the utilities available, especially water and sewer.
The land purchase agreement with the prior owner(s) should be with continuances such as zoning approval, favorable environmental study results, and utility availability.
Verify that the purchase option or agreement will give you enough time to do the above items. In most cases, one year will be favorable.
Churches may also want to consider purchasing existing property with large vacant buildings to be renovated. This may be a viable option, but consider the initial cost of property, renovation cost, and location. Verify the environmental status of the existing site and building.