Triggering build of a project 'B' from another project 'A'

Let’s say I have multiple projects, A, B, C, D and E.
Out of these projects, Project B creates some project specific configuration files which is used by all other projects, A, C, D and E.
What do I use in my .gitlab-ci.yml file so that every time I build projects A, C, D and E, every project automatically triggers project B build and be able to use the files created for deployment pipeline?