1. If you don't already have one installed, you will need to download and install Oracle or Open JDK 8.

2. If you don't already have it installed, you will need to download and install the latest Maven 3.x.

3. Download the latest sources from github: https://github.com/jbdevstudio/jbdevstudio-product/releases/tag/jbdevstudio-10.3.0.GA

4. If building offline, you will also need the latest (or an equivalent) JBoss Tools update site zip, available from http://tools.jboss.org/downloads/ or http://tools.jboss.org/downloads/overview.html

5. Unpack the sources zip or tar.gz. If you're on a Linux-like operating system, you may need to `chmod -R 755 *` in the folder into which you unpacked it.

6. For an offline build, run `mvn clean install -Plocal-sources -Djbosstools-site=jar:file:///path/to/jbosstools-*-updatesite-core.zip\!/`

7. For an online build, run `mvn clean install -Plocal-sources -Djbosstools-site=http://download.jboss.org/jbosstools/neon/stable/updates/` 

8. Note that for a GA release, you need to also use a `-DBUILD_ALIAS=GA` flag. For pre-GA releases (eg., AM2) this is not required.

    mvn clean install -DBUILD_ALIAS=GA -Plocal-sources -Djbosstools-site=jar:file:///path/to/jbosstools-*-updatesite-core.zip\!/
      or
    mvn clean install -DBUILD_ALIAS=GA -Plocal-sources -Djbosstools-site=http://download.jboss.org/jbosstools/neon/stable/updates/

9. For additional commandline flag options when building, look in the pom.xml file in the `jbdevstudio-product-jbdevstudio-*` folder.

10. Once built, look for `target/` folders, such as `installer/target` or `site/target` for the resulting built content.