I cannot figure out what a) is depicting.
My best guess is shown below, but the top view is missing the blue surface.
You can construct a solid from b) without having to add any missing sketch lines.
First is the skeleton for the model based on the orthographic views
and the solid with faces color-coded.
Note that the above involves some not-very well-defined surfaces (green) being a ruled surface resulting in a hyperboloid.
An alternative construction that is not a single solid body, but rather two triangular wedges on top of each other.
As you can see the given info can be interpreted in multiple ways. Typically features are made of simple shapes (planes, spheres, cones, doughnuts, etc.) and a good drawing will make it clear what the design intent is by providing additional detailed views to clarify any ambiguities.