When I cut a pair of fitted pants, I add seam allowances in the following areas and adjust the pants as I sew them.
Side seams: add 1"
Front Crotch: extend 1/2" to 1 1/2" This'll depend on how full your thighs are.
Back crotch: extend by 1" This is dependent on how big your derriere is.
Hem allowance: add 1 - 2".. just in case you decide to wear a heel.
Baste and sew as you fit pants. Hope this is useful.