Before building geronimo eclipse plugin(gep), you need to build geronimo server first.

Suggest you start with a released code tree to build gep, not the trunk code. Generally, trunk code is changing and unstable.

For a better understanding what you are doing, pls tell:
1. which version of geronimo you are going to work on?
2. what jdk you are using to build gep?
3. Any error when you are building geronimo server?