For me it was to my 31st birthday. Barney enters the apartment where Ted is still trying to design a building. You made me a surprise party? (Marshall goes on the roof) Super... I feel for you. Robin: But no.
Plan: A: his architecture firm; Q: What is Ted trying to keep afloat by working all night? A: Marshall; Q: Who tries to lure Ted to the roof for a surprise 31st birthday party? A: a surprise 31st birthday party; Q: What is Marshall trying to lure Ted to the roof for? A: Robin; Q: Who learns about Barney's feelings for her? Summary: Ted is trying to keep his architecture firm afloat by working all night, but Marshall tries to lure him to the roof for a surprise 31st birthday party. Robin finally learns about Barney's secret feelings for her.