Do I need to have worked overseas before?
Whatever position you apply for in your career, experience is always looked on favourably and working overseas is not any different.
The first overseas assignment is typically the hardest to get, as employers are always uncertain whether someone who has not worked overseas before will adapt to working in a new country, so far away from their friends and family. Locations such as the Caribbean are considered ideal for applicants looking for their first international assignment as employers like fresh UK experience, rather than long term expats that are maybe not up to date with recent UK construction practices, etc.