Diodes Incorporated has a 3 section on their website with a list of all of their package/case drawings. Some of the package/cases also have the step files for them. Drawings will have the dimensions as well as a recommended land pattern our pad layout. Below are 2 links with links to individual package drawings, and a document with multiple drawings:
Diodes Inc Drawings:
Pericom Drawings:
BCD Drawings: BCD Drawings.pdf (3.0 MB)
Mechanical Dimensions (diodes.com)