The most common approaches used in solid modeling are :
Extrusion or sweep: This approach comprises sketching of a cross
section on a plane and stretching it through a curved or straight path.
According to the path, you can have solids of revolution and straight
extruded figures. The cross section can also have inner loops bulging to
hollow shapes. The distance can also be provided for having straight
extrusion.
Constructive Solid Geometry: This approach makes use of various
boolean operations like intersection, union, difference on pairs of
simpler models to construct the desired shape. To initiate the modeling,
this technique is provided with a inbuilt library containing solid
primitives like torus, cube, cylinder, sphere, cone and many more. Any
selected figure is instantiated by specifying the values of its
location, orientation and dimensions. The model which is created finally
is combined with other primitives or solids to eventually get the
required shape of the component. At last, the models are represented in
a CSG tree that shows the primitives and steps used for making the
model.

Parametric modeling: Some of the recent systems use this kind of
modeling technique. In this technique, the user can specify
relationships between geometric elements. Standard shapes of casting and
tooling features can be covered in terms of few selected parameters. The
proper shape is automatically constructed by giving the parameter values
which are involved.
Other special techniques: This comprises analytical surfaces,
lofting and shelling. Analytical surfaces are helpful for defining
curved surfaces, lofting includes defining number of cross sections and
further joining them using an analytical surface. For creating an offset
surface, shelling is used.
Including experience as well as training, designer
must have the deciding strategy in regards to a particular modeling
technique which needs least number of steps. It may happen in some cases
that after retracing the steps during modeling, designer has to take a
different approach to complete the shape. Even an experienced designer,
sometimes take many days for creating the model of a complex casting. In
general, most of the castings require a combination of all techniques.