“盖” is spoken, with the top of the building above said "cover", "建" is a written language, any building can be said to "build". For example： a house, can be said that“盖房子”，and also can be said that "建房子“, but said garden, can only say that”建园林“, can not be said that“盖园林”.

盖房子 基本等于 建房子。 但是 盖房子 有种暗示盖的是小房子或者平房（只有一层）的感觉。 建房子有种建造大楼的感觉。

有房顶(roof )的用盖和建都可以，没有房顶的要用建。盖是口语，建是书面语。Hope it can help you.))

盖means putting something on top of something. 建 means to build.

“盖房” 和 “建房”意思一样。但盖/建单独存在时意思不同。