I was messing with ADE yesterday,looks like ADE won't allow you add or change terrian in enviroment?
How would I go if say I want to make an Island in the ocean with my own terrian data and mesh?
I was thinking use 3D Software and somehow can convert it to BGL? I have really no idea where to start with this, sure some comerical develope group has done this before. 

Any clues ?

I do not think any developer is going to come into this forum and give you step by step instructions on how to create terrain and mesh in the ocean.  We set up this forum for "developer to developer" interactions.  You could try to ask your question in our scenery design forum but FSDeveloper's website has many topics about this already as well as how to develop terrain/mesh/scenery - http://www.fsdeveloper.com/forum/threads/creating-islands-for-fsx.432200/.  There are many other topics about this across the Internet (including here at AVSIM) by searching - https://www.google.com/search?q=how+to+create+terrain+in+the+ocean+for+fsx&ie=utf-8&oe=utf-8

Best regards,

Jim