Many large companies think about customized enterprise software hoping to realize some special benefit. This is, in my opinion, the eighties style of buying software. There are naturally advantages to this approach if the problem that you are trying to solve has not been solved before.
But if there is even a partial solution available, we would suggest that you think about buying the license rather than embarking on custom development.
The reasons are below:
1. Difficult and time-consuming to develop: Requires scarce resources of talented developers and business analysts and your own company people should be able to provide the relevant inputs.These resources are generally not available aplenty leading to project failures or at best, project delays.

2. Difficult to champion: Who do you point to as a successful case study? As the software that you are buying is specific to you, you cannot cite prior success. Hence you could face resistance from other people in management.

3. Difficult to maintain: Needs change with time. You need vendors who keep updating themselves to keep up with the market, rather than a vendor who depends on your income to update your software.

4. Difficult to support: Once custom software is in place people need to be hired, trained and retained specifically to retain it

5. Overly expensive: Once you get in development and maintenance mode, your costs sky-rocket as the days tick by.

6. Vendor lock-in: You are now locked in to the vendor and technology and his/her capabilities.

Packaged products solve all the above issues. Most importantly you can get a sense of exactly what you are buying.

If you think an off-the-shelf product only solves half your problem choose one which integrates with another rather than trying to start from scratch.