This is a short note, that I wrote some short and concise wiki pages on LibreOffice development on Ubuntu. Please dont tell me that there is way more info on the TDF Wiki, thats true — but also not the point: In fact, there is quite possibly too much information on the TDF wiki 😉. So this is the stripped down info on what you really need to know to start working on LibreOffice on Ubuntu:
Also note the older page by Christopher M. Penalver about Bug Filing against LibreOffice on Ubuntu:
completing the bunch.