  MARTY is a C++ computer algebra system specialized for High Energy Physics
that can calculate amplitudes, squared amplitudes and Wilson coefficients in a
large variety of beyond the Standard Model scenarios up to the one-loop order.
It is fully independent of any other framework and its main development
guideline is generality, in order to be adapted easily to any type of model.
The calculations are fully automated from the Lagrangian up to the generation
of the C++ code evaluating the theoretical results (numerically, depending on
the model parameters). Once a phenomenological tool chain has been set up -
from a Lagrangian to observable analysis - it can be used in a model
independent way leaving only model building, with MARTY, as the task to be
performed by physicists. Here we present the main steps to build a general new
physics model, namely gauge group, particle content, representations,
replacements, rotations and symmetry breaking, using the example of a 2 Higgs
Doublet Model. The sample codes that are shown for this example can be easily
generalized to any Beyond the Standard Model scenario written with MARTY.
