create a box in your top view convert down to a poly go into the polygon level now select the top of the box and bevel the top of the box downwards
unselect the polygon level go to the move tool right or click on that this will bring up the snaps and grids settings make sure you uncheck (untick) the snap by grids and change that to snap by vertex. Close that down
under the edit geometry go to the quick-slice turn on your snaps, in the top view you see the inside lines
Create a box give the box 2 lenth segs make sure the lines go across the box from right to hight. convert down to a poly select the edges and click on the segs and under edit edges click on the chamfer square box now take it out to about 0.04 for example. Now select the polygons select the 3 faces (poly) under the edit geometry select deattach
now go back to the top of level H key now select the object and move the move the object out in the left view go back to the polys the polys
This is how to model a LCD TV for any room for your building.
1) select the p.view and then go to the views menu save active perspective view. this will store it to your computer memory. select the wall and now isolate by left (right) click, You'll get the drop down menu at the top choose isolate now this will isolate wall from the scene.
2) go to geometry use the drop menu choose the Extended Primitives check the autogrid now create the ChamferBox draw it on