If you are planning to buy property, build or modify and resell for speculation, then you are not talking about "local" houses but rather, properties intended for sale to expats.
Property in Belize is very very expensive, especially on Ambergris Caye and building costs a(to hurricane standards) are very high. Unless you have a few hundred thousand dollars that you can afford to risk (and I do mean RISK, that means you can afford to lose it) you should forget about coming to Belize on any basis other than as a retiree.
Belize does have an attractive retiree program, but unless you have a lot more going for you than your social security check, you can forget about Ambergris Caye, because you cannot live on a social security check on Ambergris Caye.
You may want to consider checking out the Corozal area, it is the most affordable part of Belize for someone who is on a moderate fixed income.
If you are a builder and want to build spec homes, you can probably find some reasonably priced lots in that part of Belize that you could build on and re sell for a modest profit. You might want to check out www.consejoshores.com
The only people who seem to be able to engage in no-risk "investing" are high ranking government officials and their "friends." That ain't you, so forget it.