Choosing Components for a Discrete Delta-Sigma ADC
The biggest factor is your quantization noise for resolution.

Since you have not given any specs, a priority to Vio and Iio offsets circuit balance , noise rejection, crosstalk, signal bandwidth and decimation ratio precise suggestions are not possible. (hence you must always start ANY design with a Great Spec)

However to achieve the performance of commercial IC's you must have many loops and higher order integration to move the quantization noise far above the signal bandwidth.  Using a circuit that integrates twice instead of just once
is a great way to lower the modulator’s in-band quantization noise. 

For instance, Texas Instruments DS converters include second- through
sixth-order modulators. Multi-order modulators shape the quantization noise to
even higher frequencies than do the lower-order modulators. 

ref: read Texas Instruments, Nuts and Bolts of the Delta-Sigma
Video Tutorial [Online]. Available: http://focus.ti.com/docs/training/catalog/events/event.jhtml?sku=WEB408001