I can't find the fillet command for walls in Custom Layout. You know, two walls as 90 degrees that don't quite meet. You want to extend or trim each so they make a 90.
If Object Snap is turned on then the walls will connect as they are being drawn. There are methods to move the wall and connect it, but overall it is much easier to delete one of the walls and redraw it correctly.
Refer to the Help document or the Online Video Training.
So, if I want a room that is a polygon with all 90 degree angles I should have the numbers ready to go before I enter custom layout. Do the math elsewhere.
I would suggest you subscribe to the eCabinets Online Training. There are several videos on wall and room creation. You also might want to purchase the "Nearly Complete Guide to eCabinet Systems" manual.
There are several sources for determining the angles of a polygon. The link below is for a clipart image of a matrix showing the angles for 3 to 11 sided polygons.
n is the number of sides for the polygon. The first part of the equation 180*(n-2) determines the total number of degrees for all sides of the polygon. Dividing by n finds the angle for a single side.
I've attached an Excel spreadsheet that provides a matrix of up to 20 sides. You can also view the formula in the results cells.
I noticed that you started a subscription to the online tutorials and cancelled it shortly after. It is about to expire, but the information regarding Object Snap, drawing walls in general and specifically drawing walls at an angle is well covered in the videos.