you will need
A Knife, with your favourite blade, (no 11 is good)
paints , hues of browns tans (i used, tamiya acylics valejjo acrylics and windsor newton water soluable oil paint.)
a file,
Glue!
most importanly a sheet of styrene or plasticard.
1) measure out the size of your wall, how big you want it, my wall was estimated at around half height for a 1/35 figure.
you need your styrene.....

carve in the basic shape of the wall.....

lightly etch in the bricks

score out the eges of your wall.

Once you are happly with the shape and size of your bricks
cut away the places where there will be mortar(the eges of the brick)
once you have done that you can start damaging the bricks, by scraping, slicing and gnawing at the bricks with your knife. it does not matter if you make a mistake here as walls are rarely ever perfectly even(depending suppose on where it is set and what time period)


Now the fun part. (PAINTS!!!!!)

base the wall in flat earth or your desired colour

when dry use buff(or agin your desired colour) to paint in between the bricks, no need to be neat here

when this is dry you canlock in the colors of your bricks, i used an oil in my colours to aid in dirtying the wall at a later stage.

according to taste, wash greens browns, whatever over the wall untill you think it looks dirty, (or clean enough)
for this wall i wasked a little green in some cracks and brushed
M.I.G pigment dark mud over the lower half of the wall, the oil in the bricks helped this to adhere better in some places more than others,

and cut it out
viola

repeat to your hearts content.