WOW! That question is way too open ended. It's almost like asking "what's your favorite color"? And even so the question was "build or buy?" and now it seems to be "build, compose, or buy?". Even so; there are still many levels of monitoring depending on what your business is:
- bare metal performance
- OS performance
- resources (CPU, Memory, Network, Disk, I/O)
- Application and service
First of all there are no complete solutions. They cost too much. There are regulations in PCI and HIPPA. It's too easy to leak information internally let alone externally.