If you want to start on something like this you can use curves to block out the main form and as mentioned in some other the other answers, you can convert the curves to a mesh and then extrude the form out. There are many videos on how to use curves for making logos so that would be a good keyword to use when searching.
(i) You can add a curve then align the curve to an axis by pressing either x, y or z followed by 0, then press Enter to set the tool options you have choosen . This will scale everything to the average point of everything selected so long as you have the following pivot option selected.
Now you can simply Extrude out more curve points by pressing e for Extrude(there is also a UI button in the Toolshelf t.
When you reach a corner, you can press v to access the Set Handle Type menu and if you select Vector then the handle will now be able to form a sharp corner as shown in the following image.
Here is 1/4 of a cinder block that has been roughed-out using curves.
In Object Mode Alt + c was used to convert the curves to a mesh.
Now you can add a Mirror Modifier set to mirror both the x and y axis's and Apply it.
Now in Edit mode the extra vertices which have been created should be removed. This can be done by selecting the unwanted vertices and using xthen d for Dissolve Vertices.
If you have difficulty removing the vertices that are at the mirrored points then it could be that they were too far a part to merge so you can use w -> Remove Doubles, and also, you will likely have to increase the Merge Distance a bit.
Now you might have to use Flip Normals after the extrude operation to have all the components facing in the proper direction.
Now you can select the border edges and use Fill. There are several variations of fill tools that can handle different situations.