Acquire a large number of photographs of the monument that you wish to replicate so that you can understand its structure. These need to be from various angles so that you can see how it looks not just from the front but also from the sides and the back. Ideally distribute these into smaller parts which will help you in making the replica later on.
You certainly cannot be, making a life size replica and you will need to scale it down. Choose an appropriate size for scaling down, depending on how big your replica is. If it is not very big, you can scale it down to one inch for each hundred feet of actual size. This will be greatly helpful to you in your task.
Make the Basic Shape
Make the basic shape of the monument with the help of chicken wire. This will be the base of the replica at which you will add more materials to give it the final shape. Make sure that it at least roughly looks like the monument you are replicating.
Make a wooden base for your replica. Make a couple of holes in the wood which should be at least half inch thick and fix the chicken wire skeleton into it. This will allow you to have a good base for further work.
Place paper mache
Put paper mache on this skeleton. It can be made by putting paper in water and the heavier the mache, the better the replica will become.
Once the paper mache has settled, you can paint the replica. The general trend is that monuments are in grey and green colour. Know the colour of your monument and paint accordingly.