One thing to remember, from a fluff perspective, is that building a Manse is expensive. It takes time, materials, laborers, tools... and if you can get someone else to foot the bill for all this, then you can also probably charge that person an arm-and-a-leg for doing so for them. Shouldn't take more than a few Manses as commissions before you can start making them for yourself. Don't know if that helps, but it's something to keep in mind!