That house looks pretty basic, doesn't it? I've been calling it the “Monopoly House” because it really looks like one of those wooden houses in an old collectible Monopoly game. It's just a cube with a pyramid on top. Now you want make it look likes something respectable. So let's add some details to it to make it look better. Don't forget to hit Tab to enter Edit Mode if you're in any other mode.
Your house needs something to sit on, right? Adding ground is a good first step towards making the house look more like a realistic object rather than one that floats in midair. To add ground, go to the toolbar on top of the Blender screen and select Add ==> Mesh ==> Plane. This gives you a flat surface that pretty well floats in mid-air because it's going to go wherever you have your cursor. So, grab it by hitting G on your keyboard and move it where you want it to go (under the house).
To put your ground exactly where you want it in the first place, right-click on any one of the bottom vertices of your house to select it, and then hit SHIFT + S. This gives you the Snap To menu, with options for moving your cursor or your selection exactly where you want it. Select Cursor to Selected to move your cursor to that point. Now add your plane, and it should be exactly at the point where your cursor is now.
Once you've added your plane, you might notice that it isn't all that big yet, so hit S on your keyboard to scale your plane. Then move your mouse left or right until the plane is the size you want. It should be slightly bigger than the area of the bottom of your house, though it can be as big as you like. If you get a little impatient, go to scale mode by hitting S, and then use the numbers at the top of your keyboard (not your number pad) to resize it by multiples of its current size. For example, if you use S and then 2, the plane will be twice as big. Be careful, though: if you use S and then hit 2 and 5, your plane will be scaled by a factor of 25! A quick Control + Z will undo any error you make. Keep an eye on the left side of your 3D View header on the bottom of the 3D View window to see the factor by which your selection is scaled while you're using the Scale tool.
Scaling can work for your house, too, if you want it to be a little bigger. One interesting factor is the pivot point, which is in the center of geometry in any 3D object by default. That pivot point can be changed by going to the 3D View header and selecting the drop-down menu with an icon that looks like two circles overlapping. This gives you options for changing the pivot point for your 3D object with the median point being the default. Select the 3D Cursor option, and the cursor can now be placed wherever you want the pivot point to be.
Here, I've deleted the ground plane for the sake of not messing up this next step. I'll re-add it once I've completed this step. Now that the cursor is snapped to one corner of the house, I can scale the house while still keeping one corner in the same place by selecting all vertices on the house. This saves the trouble of having to move the house back into position after I've scaled it to my preferred size.
Adding An Overhang
So the house still looks like Monopoly House, basically a cube with a pyramid on top. We can change that by adding an overhang to the roof. So, let's go back to the pivot point. First thing you want to do is select the very top vertex on the roof. Move the cursor to that vertex by using SHIFT + S and selecting Cursor to Selected.
Once you have the cursor on the very top of the roof, you want the ability to select edges. This can be done by going back to the 3D View header and selecting the Edge Select button that looks like a cube with one edge highlighted. Now you can select edges, which will be highlighted in white. If you select multiple edges, the most recently selected one will be white and other selected edges will be orange.
Now, select all the edges along the bottom edge of the roof. Now, hit E for extrude and then S for scale. Now you can extend each edge you selected and each extrusion will be to scale. This is called scaling uniformity. Now you can extend your overhangs as far as you like (as in the above picture) and each side will remain scaled to one another. Because real roof overhangs don't come out very far, you can just extend them a little and then set them by using the left-click button on your mouse.
Working With the Faces
Now, we want to work with the house's faces, so we go down to the 3D View header and select the Face Select Mode button. Now you'll see that there are little black squares in the middle of each face. These aren't actually vertices. This is where you designate the front of your house. What I like to do is rotate it to positive-X. Essentially, the red axis arrow on the bottom left corner of the grid view will be pointed toward me. Select the three faces that are now facing you, as in this picture:
Now rotate the view slightly to the left or right so that you can see what you're doing. Extrude those three faces as far along the X-axis as you like (hit E, and then hit X to lock it to the X axis):
If you like, you can choose exactly how far you want to extrude the front, using the numbers along the top of your keyboard. For instance, hitting 2 will extrude the front by two Blender units, as measured by the grid on the 3D View window.
Rotate your house some more, and you'll notice that you have some extra edges inside the house. If you intend to add more dimensions to your house, you could leave the exterior ones, but those interior edges could be deleted. To do that, go back to Edge Select Mode and make sure you're in Occlude Geometry Mode so you can actually see the interior of your house. For now, I'll just delete the original “bottom edge” of the roof that is now inside the house as no longer needed, by selecting the edge I want to delete and hitting X or the Delete button. This will produce the Delete drop-down menu. Click on the Edges option to delete your selected edge.
Creating Doors And Windows
Now you're probably wanting to create some doors and windows for your house. For this, you use a process called subdividing. Basically, you're converting parts of the faces into the elements you want. Return to Face Select mode and select the faces of your house, including the new ones that you just created. (Just a tip: Click as close to the black square on the one you want to select to make sure you get that specific one.) Hit the W button to bring up the Specials menu and select Subdivide. This will cut each selected face into four equal parts by default. We'll need more than that to create the doors and windows, so go to the Mesh Tools menu at the left of your screen and look for an option called Number of Cuts. If we do 9 cuts, it will actually divide up each face into a 10 by 10 grid.
Now, deselect everything and zoom into one of your walls, as close as you like. Disable the Occlude Geometry feature by hitting the Limit Selection to Visible button on the 3D View header to make your life easier. Select several conjoining faces in a rectangular shape. Now, extrude them inwards just a little. You can get better control of this by hitting E, then X or Y depending on which side of the house you are working on, and then entering 0.1 or -0.1 (again depending on side) to push the faces inward by one tenth of a Blender unit. Hit the Enter key to lock it in.
Looking More Like A Real House
So that's my first window on my rudimentary house. It's looking less like a Monopoly house and a little more like a “real” one. Repeat the process of selecting faces and extruding them inwards to create more windows and a door or two as appropriate on each wall.