It sounds like you need to go to the "Abilities" tab and look up "Drone - Morph Unit (Drone -> Zerg Buildings)" then under the abilities tab (or "Ability - Info +" if you're in table view) it has a list of all the ability commands which are different buildings you can morph into. Just double-click an empty slot and select the button, requirements, Info-Unit, and Info-Time and that should be all you need to fill out there I think. Now you should find it as an ability command when you try to add it to the drone's command card. However the name on the command list will be the name of the button you selected. For example if your new building command uses the baneling nest button that means when you try to find the ability commands on the list for the command card it will have both "Mutate into Baneling Nest" for the real Baneling Nest and "Mutate into Baneling Nest" for your custom building, because they both use the same button. Of course you can create your own button or maybe there is already a Lurker Den button you can use.
@nuxar: Go
When adding an ability to the CC, remember you first select the container ability, in this case, the Morph Drone > Building, or whatever.
Then on the next pull down, your lurker building will appear.
@DarkShape80: Go
Yes, I did do so but still no lurker...
It sounds like you need to go to the "Abilities" tab and look up "Drone - Morph Unit (Drone -> Zerg Buildings)" then under the abilities tab (or "Ability - Info +" if you're in table view) it has a list of all the ability commands which are different buildings you can morph into. Just double-click an empty slot and select the button, requirements, Info-Unit, and Info-Time and that should be all you need to fill out there I think. Now you should find it as an ability command when you try to add it to the drone's command card. However the name on the command list will be the name of the button you selected. For example if your new building command uses the baneling nest button that means when you try to find the ability commands on the list for the command card it will have both "Mutate into Baneling Nest" for the real Baneling Nest and "Mutate into Baneling Nest" for your custom building, because they both use the same button. Of course you can create your own button or maybe there is already a Lurker Den button you can use.
Hope this makes sense 8)