Thanks mate.
Okay so I am still busy with trial and error, learning quite a bit in the process, what I like about this is you can do the box model, subdivide as a parent mesh and continue editing the box shape, which automatically updates to the parent mesh, so you can get a clear indication of what the end result will look like. also manage to cut the polygons from 4000 to 909 without the roof so definitely will be making it longer with more side tunnels to explore.It is quite time consuming so will likely only be doing the one cave, I want to take a tunnel below the terrain so you wade trough the water, should that float your boat.
The biggest issue I have encounter is getting the main section to seamlessly snap with the main corridors of the base, but I have a solution to that problem with making a much smaller access tunnel and enter the cave from the sides instead of the main area of the cave, It also gives bigger scope to the cave definitely keen on getting this right, which would mean future packs will include similar cave system to explore.This learning curve is also a step towards creating isometric caves.
Excited to see the final product, will likely keep me busy for the rest of the week as tweak it.
Win7 pro, Intel 2500K @3.7ghz 660GTX 8gig ram 16tb HDD