I have completed the main quest line for the thieves guild, and when doing a quest for Vex where you have to break into a house and get an item, (Hemskeirs House in Whiterun, sorry if i misspelled his name) the door is blocked by rubble and the house has a broken roof. Any known fixes? I cannot become guild master without completing this quest.

Just return to the quest-giver and quit the current job without any penalties. !!!!

Just a failed quest in the quest log. But yes, simply returning to your questgiver and quiting your quest should fix it.

Those quests really shouldn't fall into the main quest log in my opinion, just because of the sheer amount of them you have to do (20 to become Guild Master, 125 to get all the trophies) really clogs up the quest log.