Currently, job-dsl-plugin supports creation of items

1. relative to Jenkins root
2. relative to the seed-job's parent folder

From my experience it is not uncommon to group several seed-jobs together in a folder (e.g. named seed-jobs. In that case, neither 1. nor 2. make sense.

With 1. you can not confine them into a separate folder.
With 2., both seed jobs and the generated items would be cluttered in the same folder.

So I propose a third option
3. relative to the seed-job's grandparent folder

That way, you can nicely organize jobs and seed-jobs for projects like this:

/projectA/foo/...
/projectA/bar/...
/projectA/seed-jobs/foo-seed
/projectA/seed-jobs/bar-seed
/projectB/baz
/projectB/seed-jobs/baz-seed

I will provide a PR in a minute.