If you haven't yet separated from your spouse but are contemplating divorce, you may wish to consider the ramifications of shared custody on child support.
Generally, full guidelines child support is assessed to the non-custodial parent, meaning s/he will pay 17% of adjusted gross income for 1 child, 25% for 2 children, etc. However, in a situation where custody is shared 50-50%, the courts often do an "off-set," meaning they'll compare the mother's income to the father's, and only assess the percentages to the difference between the 2 incomes. This could potentially result in a significant savings for the parent who would otherwise be the non-custodial parent.
How do I get shared custody then?
Begin now by taking an equal role in the children's lives. Share the responsibility of ensuring the kids get to school, extracurricular activities, doctor's appointments, etc. If your spouse has more time on his/her hands than you, then suggest s/he take up some activity which gets them out of the house. Have the kids then spend time with a relative or sitter if you're not available. This serves to more equalize the actual time each parent spends with the kids. There may be other ideas as well, so you're best advised to sit down with an experienced family law attorney today to plan for tomorrow!