First of, can we see a picture of what you have ?
Have you model it, one wall one object ?
If so, you apply a UVW Map to the object.
(Found in the Modifier menu -> UV-Coordinates
or in the
modifier list that you get access to when in the modify tab)
Then press M to get to the material editor.
or click on the icon with a yellow, a red and a blue ball.
Click New - > Standard
Next you need to attach a diffuse map (color map or brick).
- You either click on the some box to the left color sample for diffuse
- or click on maps, then the
Map slot left of the diffuse.
Next you need to apply the material, click on Apply at the top.