Rocks and boulders for a roof terrace

A customer asked for some bespoke rocks and boulders for a roof terrace.   A new mould for a 1.2m tall x 800mm wide rock worked out to around £ 2800.00 plus vat and I suggested using our existing rocks and tall stones instead.   My suggestion differed from the original layout but sometimes compromises have to be made.   Here is my suggestion: