Change grid size for larger drawings

Hello,

 

Got Draftsight figured out to create parts drawings where the grid points are 1/2" by default. Need to create some drawings for shelves & cabinets which are 20" or 36" etc. How do I change the grid points or drawing area to handle larger items yet still be able to click on the end points and give the dimensions? I created a line 20" long and it extends way beyond the edge of the screen.

 

Thanks