Finding a plot of land and building your own property can be a very good option. The difficulty nowadays is finding a good quality lot in a prime position. There is now very little quality land left on Isla Mujeres. Where you can still find lots for sale is on the Caribbean side of the island, there are Americans and Canadians who prefer this side of the Island. It has it's advantages, especially in the summer when the wind that comes in across the Caribbean cools everything down and certainly keeps the mosquitos away. At other times of the year, it can become annoying; windows need to be constantly cleaned due to the salt and lush landscaped gardens are not an option, although cactus does quite well.
The main disadvantage is if there were to be a hurricane. We have been very lucky, with no hurricanes since Wilmer in 2005. At this time some houses on the Caribbean side of the Island were devastated when Wilmer struck, this is where the brunt of a hurricane is felt. This was in part due to lack of preparation, people had become a little complacent, some didn't even have hurricane shutters and all that was left of their house was just a shell, what we call "Obra Negra". People had effectively forgotten about hurricanes.
There hadn't previously been a hurricane since Gilberto in 1998, which hit land at Puerto Morales. Normally once a hurricane reaches land its force is reduced but not Gilberto, the island suffered terribly as did Merida and it was still raging when it hit Progresso. If you decide to build on the Caribean side of the island, which is effectively the only place where there is quality land with sea views available, it is important to be prepared.
The next step is finding a good builder, most people have heard of the horror stories here on the Island of Americans and Canadians who have arrived on the island with no prior experience and perhaps jumped a little too quickly into coming to an arrangement with a builder, only to find they have not only been grossly overcharged but in some cases having extracted the maximum they can from the client left the property unfinished. We often hear much criticism of Mexicans and their lack of seriousness, however, the two main perpetrators of this damage done to these people in recent years and the reputation of the island are two people neither of whom is Mexican.
The most important factor is to do your research, talk to local people, they know who the dishonest and honest builders are, or talk to Mundaca Real Estate, they have been on the island a long time and they are decent people. It is very easy for someone newly arrived on the Island to get drawn into dealing with the wrong people. Ask them to show you all their previous work, not just what they want to show you, then separately try to speak to their previous customers and find out about their experience, this is where the cracks will appear; sometimes literately.
Another trap many have fallen into is extras, they are suddenly presented with a bill for extras of which they were totally unaware. Is often comes about as a result of suggestions by the salesperson such as "Why don't we do this?" or "It will look nicer if we do it this way". To the unsuspecting client, these are just helpful suggestions but in reality, it is what ends up as a very large and unexpected bill. The way to avoid this is to have a Catalogo de Conceptos, this is a document of about fifty pages drawn up by the Architect who draws up the plans which list all the material to be used, down to the last bag of cement and all the labour costs. Once the builder has completed this and it has been checked and approved by the Architect, their hands are tied when it comes to ambushing the client with extras. Stage payments should be set and paid as the work progresses, there is absolutely no reason why a client should pay the builder $100,000 at the start of the building process, as has happened, or indeed any large sums in advance.