Don’t build or buy
All of us have heard the old chestnut "Build vs Buy". As a way of starting a conversation about software decisions it’s fairly unhelpful. Firstly, it’s a false opposition. If you choose to build, are you going to build everything? Chances are you’ll build on top of something else. (And the buy part should really be "license", since not all software needs to be purchased.)
So, what we really should be doing is assembling: using stuff we already have, licensing bits we don’t have but need, extending bits where necessary and assembling it.