We could add all windows and doors to the building using the hole tool. However, there is even quicker method available: drag and drop from object libraries.
Modeling in shaded perspective view is fun but often the best accuracy is obtained by using parallel projection and a wireframe view. So, alt-double click the view to get back to the quad view and then alt-doubleclick the top view to maximize it.
To find a good zoom scale for further modeling, switch to the leftmost geometry tab of the select window, drag the building object and drop it into the view window. Dropping an object to view performs an Auto Focus operation. The view window will zoom exactly around the selected target. You can also use the Auto Focus tool in the view control bar after selecting the building.
The loaded window and door items should go under the building hierarchy. Therefore, click the 'Building' object in the Select Window. The current level marker jumps from the root to the building level. Then select Browse Object Library from the popup menu. This opens the loader window, which shows disk library objects conveniently as small thumbnails.
Click the library folder called furniture, and find the item door. Drag the door icon over the view window and drop it just outside the point where you want to insert the main door of the building. Do not drop it too far away from the wall; the door has auto-snapping properties, which become active if a wall surface is found closer than one meter. If the drop position was correct, the door snaps exactly to the wall and rotates itself to the direction of the wall.
The loaded door object appears in the view window and in the select window's hierarchy tree. It is automatically selected and displays useful attributes in the toolbar. Try changing the width to 1.2 meters.
Next drag and drop another door for the small closed room in the upper corner of the house. The width of this door can be smaller, say 0.8 meters - change it using the toolbar control. Then drag and drop several windows so that every wall and room gets at least one window. Note that you have to drop the windows outside the building; otherwise the outer mouldings of the window may rotate to the wrong side of the wall.
Close the loader window and take a front view. The windows are quite small; let's make them bigger. In the select window, drag a selection box around all objects called window. You can also select them all by clicking them one by one holding down the Shift key, which is the multi selection modifier.
The windows are parametric objects, which automatically display the dimensions in the tool bar. Change width and height to 1.2 meters. If the upper edge of the windows got too high, simply drag the green translation axis downwards on the view window. Note that holding down the Shift key releases grid snapping temporarily and allows you to align the windows with the upper edge of the door.
Before proceeding into other steps of building construction, let's clean up the hierarchy. Multi select all doors and windows, and select Drop to a level from the popup menu of the select window. The selected objects are placed under a new folder. Use the Rename tool of the popup menu to rename the folder as doors_and_windows and close the folder. This action keeps your scene hierarchy more compact and better manageable. You can naturally later open the folder, select and edit any door or window if you like. Then save the project with a new name.