Join elements and attach walls to roofs
Join walls and attach tops
Why it matters. Unjoined walls show a double line. Walls that should stop at the roof still run through it. Join and Attach Top/Base are different clicks, easy to mix up.
What VI MCP does. Join where they meet. Attach a wall or column top or base to a roof, floor or ceiling. A query can tell an attach from a join before you write.
Try this prompt
“Join these walls where they meet, then attach their tops to the roof.”