Re: LAYOUT
Custom Design --- This means the complete physical design layout is done manually. Even the cells or libraries are done manually. This method is mainly used if NRE cost comes out to be very low.
Semi-custom-- Here, some part of the layout is done by EDA tool viz. ASTRO,Soc Encounter etc. and to get the optimized results we do it manually. The vendor gives the std. cells and libraries if the tech. needed for the design. Designer needs to be very proficient with the tool and it's good if he has good understanding of algorithm running in the tool
I hope it helps... you!!