curtain wall panels join

[alobodin]

How can I make one panel long and another panel short?

[barthbradley]

Why don't you put a "L" corner Mullions on one wall and delete the end Border Mullions on the other wall.  Bada Bing! 

[barthbradley]

...or Disallow Join and drag the ends to where you want 'em.  

[ToanDN]

Disallow join the two curtain walls and manually stretch their length to where you want them end.