I teach enterprise systems at a university, with emphasis on SAP. It's hideous. Hideous. My students complain it is unusable (agree), doesn't make sense (agree), that they can't see the point (agree). When you look at the underlying database 'schema' (inverted commas deliberate) you'll find it's a massive, denormalised mess. Much of what SAP can do can be done at the local level using intuitive software. Reports, for…
That is my goto advice on buy vs build. If you buy, then you should be willing to change your business to fit. Otherwise you should build. The more you resist changing your business the more you should build. The more you don't want to build, the more you should be willing to adapt.