Join

Combines a series of finite linear and open curved objects at their common endpoint as a single object
Lines, polylines, arcs and elliptical arc can be join as a single object.

The exterior walls are separate lines

Freeze the Column layer, Hidden layer and Wall_Interior layer

Home tab > Modify panel expand > Join

Cross-select all exterior walls
Press [Enter]

All exterior walls join as a single object

Thaw the Wall_Interior layer

Home tab > Modify panel expand > Join

Cross-select the interior walls for bedroom and restroom
Press [Enter]

Both rooms join as individual polyline object

Home tab > Modify panel expand > Join

Cross-select the kitchen walls
Press [Enter]

Kitchen walls join as a single object

Thaw Hidden layer

Home tab > Modify panel expand > Join

Cross-select lines for study area
Press [Enter]

Multiple lines join as a single object