Joint venture agreement is executed in case of commercial collaboration in which two or more unrelated parties exchange, or integrate some of their resources with a view to mutual gain, while at the same time remaining independent. Whereas a builders agreement agreement is with the builder which details the various costs that may be incurred for buying the house. This would include the cost for utilities like electricity and water, parking space, various taxes and in some cases even the registration charges. You need to execute a builers agreement with your builder.