I like to build a patio near my pool. I would like to span 27' without using interior post. What size glue-lamb would I need?

Glu Lam beams are sized by knowing loading details. You gave us no information. I can tell you that 27" without at least 1 support is going to be a very big beam and you will probably need to install a footing under the end supports. You could be in Alaska with extensive snow load or Key West. Best left to the engineering of the company that will make the beam.

Even my little rural lumber yard has an engineer do the calculation, given all the information needed. Plan on around $500 or more.