Hi rufb
Bellow there are some recommendations:
1) I agree with Keith; The layout of bipolar and diode devices are often provided by foundry, and it comes in the design kit. In every CMOS processes that I have worked, the layout of these devices was already available. And it wasn’t possible to design the layout.
2) One fundamental recommendation is to draw the bipolars in a common centroid configuration. And for this reason, it is usually preferred to use aspect ratio of 1:8, instead of 1:10. The attached figure is from my last design; you can see that all BJTs have common centroid.
3) It is also very important to match the resistors. For this, you can use the configuration also shown in the figure. Note the there are two dummies resistors.
4) It is important to choose the proper material for the resistor. It is a tradeoff between: temperature coefficient, resistance per square, matching, etc. In my design, I used P+ Poly resistor, with of TC = 160 ppm/°C
If you have another doubt, you can ask.
Palmeiras,