extrude from multiple surfaces

Hi There,

I am trying to create an extrusion from a flat surface and I need the extrusion to begin only from the flat surface and any intersecting angled surfaces. Figure1 shows the extrusion that intersects from surfaces.  Figure 2 shows how the extrusion in only starting from the flat surface and not from the angled surfaces.  The result shown in figure 2 shows that the extrusion goes beyond the body of the part. 

Is there a way to get the extrusion to start only from the flat bottom surface and the angled surfaces that are intersected?

Thanks

SolidworksSketching