Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Technie Collider Creator Free.
Technie Collider Creator v1.9
Need fast, accurate physics?
The Technie Collider Creator lets you quickly create accurate colliders for the most awkwardly shaped objects.
Simple, Intuitive Workflow
Just select your object and start painting what you want your physics hull to contain. Add as many hulls to an object as you need to get the accuracy your game requires.
Of course, prefabs are supported!
Handles Tricky Objects
Because it’s entirely user driven, tricky objects are no problem. Make robust colliders for hollow objects, spindly objects, arches and other awkward shapes easily.
No components needed in your final game – just nice accurate colliders generated in the editor for you to handle how you want.
Supports convex hulls, boxes and spheres for the best fit. Then rapidly set up your colliders with physics materials and triggers.
Try out our new ‘Face’ feature. Create solid colliders from flat faces or triangles. Great for Quads.
Support for SpeedTrees
And just added – ‘Span from Selection’ and ‘Generate Colliders from Selection’ – intelligently and very quickly generate box colliders for multiple selected objects. Perfect for rapid collision markup in levels.