Hello, you should build your building only on the server and not on the client. Use a Custom Event and set “Run on Server” Then Spawn your building. Make sure that your building is Replicated (Go in Class defaults of your building and check Replicates).
I encourage you to download the Unreal ContentExamples and look at the Networking map. You can find the ContentExamples project on the “Learn” tab of the launcher. Also check this for informations on Replications : Networking Content Examples | Unreal Engine Documentation