Estimating building layouts using exterior radar measurements is a challenging task involving electromagnetic modeling, many unknown parameters, and a limited number of sensors. We propose using the jump-diffusion algorithm as a powerful stochastic tool that can be used to estimate the number of walls, their unknown positions and other parameters. We develop an efficient iterative procedure that first uses low-frequency transmissions to obtain rough estimates of the building layout. These estimates are then used to initialize the estimation at higher frequencies, thus obtaining more accurate results. We show that with proper frequency selection, the building layout can be estimated using radar measurements at only a few frequencies. Numerical examples are used to illustrate the performance of the proposed algorithm in practical situations.