Agricutural Buildings(ABA) & Capital Allowances

I have a client who is a large farmer and a few years ago in 2008 spent considerable expenditure on constructing new cattle sheds.
In total around £700k was spent on this and out of this roughly £250k was put into the general pool for capital allowancs of which
some £140k qualifying immediately for first year allowance(as this was prior to AIA). Out of the remainder roughly £375k was put into
Agricultural Buildings Allowance pool qualifying for 4% ABA in that year. The remainder of this roughly 75k was put into fixed assets under freehold additions and no capital allowances were claimed.
My query is that I am now considering whether more of this expenditure would have qualified as plant and machinery rather than ABA
as ABA has now been done away with.
So what types of items within the cattle shed would qualify for plant & machinery capital allowances?
Also can I go back this far to 2008?
Should I get an outside expert in this field to visit the farm premises and look at what qualifies as plant & machinery and what
doesn't or could I do this myself?
Any answers are much appreciated in advance.