Sketchup and Maya seem to be the two CAD programs that have a lot of trouble making solids.   When you merged these parts it kept the inner walls (which shouldn't exist).  The red means there is an odd number of walls passed through if you trace a line from your eye to the red areas and beyond.  That should never happen.  never.  It means it's not a solid.   I don't know maya so I'm not sure how you fix this.   Did you try slicing it anyway to see what it looks like