How to draw logic gates in conformity with official standards?
The document you need is IEEE Std 91a-1991, "Standard Graphic Symbols for Logic Functions". The 1991 revision is supposed to conform to IEC 617-12 and includes IEC symbols. In particular, I think you want to look at Annex A, "Recommended Symbol Proportions".

Other standards that may be helpful are ANSI/IEEE Std 991, "Logic Circuit Diagrams", and IEEE Std 315-1975 (ANSI Y32.2-1975, CSA Z99-1975), "Graphic Symbols for Electrical and Electronics Diagrams".

These standards are available from the IEEE.