Snap to grid.. other options?

Snap to grid doesn't really work for some of my designs. Was trying to do a design line segment by line segment. Is there a way to snap to a part or line?
Was making a basic box that was 10" top line and and 7.5" on the bottom and a 5.5" line connecting them at an angle but I didn't know the angle so that is all I had to go off of.

 

See the video on node editing link below, best way to do this is to draw a box 7.5 wide and however tall you want it, convert to poly arc, double click on the box to edit the nodes. Click on the divide tool then click on bottom line of square, enter the # of nodes you want to create such as 2, it will create two additional nodes evenly spaced. Then you can use node edit to space the inner nodes exactly 1 inch inside from the outside corner nodes, then delete the outside corner nodes and your bottom line will now be 5.5 inches.

Or if you had V9 of TM Cad you could use Custom Parts and choose the Trapezoid shape

https://torchmate.com/university/tmu-11-node-editing