Some block shapes won't convert into a standard DesignBuilder block and turn brown in the model viewer when you try. A typical error message is:

Error: Can't fit block slabs

This can sometimes happen after having cut an outline block or having used the boolean geometry tools to create a complex outline block. The problem occurs because all vertices (corners) must only be in contact with a maximum of 3 surfaces; any more and the algorithms used to create zone inner volumes cannot work. Where possible, the software will attempt to introduce an additional surface in order to convert non-compliant vertices but sometimes the vertex topology will not allow this. 

The problem will be resolved later in the year with the introduction of a new block type with "paper-thin walls". This will allow any geometry to be created in DesignBuilder, which will be very powerful. Until then it is necessary to work within the limitations of the current system, which means that some more complex outline block shapes may not convert successfully into building blocks. In some cases it may be acceptabe to manually cut a failed block, ensuring that a non-compliant vertex lies on the cutting plane, in order to create two outline blocks that will convert.

It should alway be possible to convert any outline block to a component block as these don't have a block wall thickness.