Adding Units to buildings

Meh, I have no idea what to do
I got a idea for a uber unit spawning system but I need help

For E.g I have the Elven Fortress based of the mercenary camp so I can buy the units out of it. However I want it to be like if I want to train the Wood Elf, I would require to have the Woodstead

Help plz!!
Much appreciated

My first post
Poka~

Try putting you Wood Elf in the "Techtree - Units Trained" or "Techtree - Units Sold" of your building, whichever you wish. (Open the object manager and find your building - the techtree options are almost at the bottom.)

Then to add requirements, find the Wood Elf in the object manager too, and add something to the "Techtree - Requirements"