There are currently many voxel based sandbox games out there. Building in these games can be very fun, but also frustrating when you are trying to create very specific shaped structures.
The Voxel Toolbox app will help by providing a guide for building both 2D and 3D shapes. Choose the shape your interested in and set the properties, such as dimension and angles. The app will then layout in a grid exactly where you should place your voxels to reproduce the shape.
Shapes currently supported are: