1. Mesh Construction
Whereas it is possible to construct a mesh by manually specifying vertices and
faces, it is much more widespread to build meshes using a kind of devices. A
wide kind of 3d graphics programs packages are available for use in assembling
polygon meshes.
Box Modelling
One of the more well liked methods of assembling meshes is carton modelling,
which uses two easy tools:
1. The subdivide tool divides faces and edges into lesser parts by
supplementing new vertices. For demonstration, a square would be subdivided
by adding one vertex in the center and one on each edge, conceiving four
lesser squares.
2. The extrude device is directed to a face or a group of faces. It conceives a
new face of the same size and form which is attached to each of the living
edges by a face. Thus, accomplishing the extrude procedure on a rectangle
face would create a cube attached to the surface at the location of the face.
http://theorangeduck.com/page/subdivision-modelling

2. Extrusion Modelling
A second widespread modelling procedure is occasionally mentioned to as
inflation modelling or extrusion modelling. In this procedure, the user creates a
2d form which finds the summarize of an object from a image or a drawing.
The client then utilises a second likeness of the subject from a different bend
and extrudes the 2d form into 3d, again following the shape’s summarize. This
procedure is particularly widespread for creating faces and heads. In general,
the creative person will form half of the head and then replicate the vertices,
invert their location relation to some plane, and attach the two pieces
simultaneously. This double-checks that the model will be symmetrical.
http://forum.thegamecreators.com/?m=forum_view&t=93981&b=3
Primitive Modelling
Another widespread method of conceiving a polygonal mesh is by connecting
simultaneously various primitives, which are predefined polygonal meshes
created by the modelling natural environment. Common primitives
encompass:
Cubes
Pyramids
Cylinders
Spheres
2D primitives, such as rectangles, triangles, and disks

3. Specialised Modelling
Eventually, some focused procedures of assembling high or reduced detail
meshes exist. Sketch founded modelling is a user-friendly interface for
constructing low-detail forms rapidly, while 3d scanners can be used to
conceive high detail meshes based on existing real-world objects in nearly self-
acting way. These apparatus are very expensive, and are usually only used by
researchers and industry professionals but can develop high correctness sub-
mill metric digital representations.
http://en.wikipedia.org/wiki/Polygonal_modeling
http://banburywalker.com/labs/labs/scan-3d-test/