Problems making a bevel

Hey guys, I’m trying to make a door architrave in blender. I want to make a bevel on the end of a long thin rectangular panel by selecting one edge and grabing it and moving the edge down so that it forms a 45 degree angle so that a horizontal piece can also be at a 45 degree angle and fit nicley together to form a perfect right angle. Is there any easy way to achieve this?

Try using Bevel modifier. If you specify Segment of 1, that will form 45 degrees bevel with want you input for the Width. Use Limit Method of Vertex Group if you want bevel of given width on particular edge only.

Youll want to use a shear function at that point.
In edit mode, top view(or side if need be) orthographic view> Mesh>transform>shear
Then slide the mouse so it shears in the direction you want.
The look at the circled box and set it to 1 or -1 and that is a 45 degree angle

Awesome thanks heaps for the reply guys