Feb,
Others can comment but I think you can have an outbuilding that has a footprint of less than 150 sq/ft as long as it is 20 feet or more from the shoreline. See the link below.
I also beleive that this is a DES rule and not a Meredith rule as it it not a permanent structure but rather an outbuilding.
We built a home in Meredith on Winnisquam 2 years ago and the town building inspector is a good guy but very, very tough on shorline management. We were doing very little to disturb the water front and we still needed to qoute chapter and verse of the state laws to complete the project.
http://www.des.state.nh.us/factsheets/sp/sp-7.htm