Trick of the Dark- Trying to build a cave

One of my responses to the cave issue and it being the crux of the film was to try and build a cave, in doing this, I went to B&Q and bought some supplies, these were, some polystyrene blocks, gorilla glue, some chisels and sandpaper and some stone effect spray paint. Me and Andrew then took all of these into the studio and began making a practice wall to see if it would work on a larger scale.
So then the first thing we did is take on of the blocks and began chiseling out chunks to form grooves and used sandpaper to smooth the corners to imitate the grooves of the rock on a cave wall.

Having done this we then took the second block and did the same so that it matched up with the piece it would be laid next to. Then at some point during the carving of this block we realised that while it was starting to shape and look quite nice, we had the issue that it would look too flat and as such it would need to have bit attached that would stick out to add the the 3-D nature. So in reaction to this we decided to sacrifice some size on the wall by cutting up the fourth block to create some bits of rock that stick out. So we cut out some shapes and placed them on some of the grooves and shapes on the wall. We then numbered the small pieces in relation to where they were on the wall and began gluing them together. The next step was the put weights on all these pieces so that they would glue over night. While this was happening, I took a spare piece and sprayed it to see what the stone effect paint looked like on it.

So at this point the wall itself it chiseled and glued so it is in the wall shape and we have a spare piece painted to see how the paint adheres to it. It is at this point I would like to evaluate the wall as an idea for the cave shoots.

Basically, shape ways it makes a fairly convincing wall, the paint isn't all that great as a blanket cover, it wouldn't match all that well with a real cave, this is defintitely possible had I planned and done it sooner to make a full set but given the time left and my ability to paint it, I feel this is where this option ceases to be one, however my main reason for this is in fact the cost, for that one wall I spent around £30-40 which was expensive for that one wall so to then push that up to a full cave we are looking at a rather large cost which I would only want to do if I was to have the perfect cave.