  We present a coupled-channel Lagrangian approach (GiM) to describe the $\pi N
\to \pi N$, $2\pi N$ scattering in the resonance energy region. The $2\pi N$
production has been significantly improved by using the isobar approximation
with $\sigma N$ and $\pi \Delta(1232)$ in the intermediate state. The
three-body unitarity is maintained up to interference pattern between the
isobar subchannels. The scattering amplitudes are obtained as a solution of the
Bethe-Salpeter equation in the $K$ matrix approximation. As a first application
we perform a partial wave analysis of the $\pi N \to \pi N$, $\pi^0\pi^0 N$
reactions in the Roper resonance region. We obtain $R_{\sigma
N}(1440)=27^{+4}_{-9}$\,\% and $R_{\sigma N}(1440)=12^{+5}_{-3}$\,\% for the
$\sigma N$ and $\pi \Delta$ decay branching ratios of $N^*(1440)$ respectively.
The extracted $\pi N$ inelasticities and reaction amplitudes are consistent
with the results from other groups.
