Planning to purchase a home in the Woodlands/Magnolia area in July, if I find a house without a pool can I convince a mortgage lender to let me roll the expenses of installing a pool into the original loan, or is this a bad idea?

I could see the possibility of raising the principal higher than I might afford the 20% down to avoid PMI...what else am I missing?

You would not be able to roll a pool into the loan when buying an existing home. You can however you close, get a home improvement loan. The rate will be higher then your first lien mortgage but also much smaller obviously. Most home improvement lenders will allow you to borrow up to 90% of the total market value with some value added back for the improvement and some will even go over 100%. This would be your best bet.

Halifax I'm with Amegy in the Woodlands. My email is on my profile. There are options if you'd like to discuss.