The Build effect works on Meshes and causes the faces of the Object to appear, one after the other, over time. If the Material of the Mesh is a Halo Material, rather than a standard one, then the vertices of the Mesh, not the faces, appear one after another.
Faces, or vertices, appear in the order in which they are stored in memory. This order can be altered by selecting the Object and pressing CTRL-F out of EditMode. This causes faces to be re-sorted as a function of their value (Z co-ordinate) in the local reference of the Mesh.
|Note on Reordering|
If you create a plane and add the Build effect to see how it works you won't be happy. First, you must subdivide it so that it is made up of many faces, not just one. Then, pressing CTRL-F won't do much because the Z-axis is orthogonal to the plane. You must rotate it in EditMode to have some numerical difference between the co-ordinates of the faces, in order to be able to reorder them.
The Build effect only has two NumBut controls (Figure 2):
Len - Defines how many frames the build will take.
Sfra - Defines the start frame of the building process.