I am a mother of 3 and am on a program that assist people with disability's in New York city .My landlord has just put the building I live in up for sale with out notice and still collecting rent is this legal

Why would it be illegal to collect rental monies? He still owns the building until it is sold. You should contact the program that got you the apartment and advise them that the landlord put the building up for sale. This could mean that their program won't be recognized by the new owner should he sell the building. The program may want to put you into a different apartment if the building is sold.

New York City landlord/tenant laws do not require the landlord to notify his/her tenants of his/her intent to sell.

Of course he can collect rent... he still owns the building right?

Actually, by law, the existing landlord has to honor your lease until the day of the closing - if and when they sell the building. AND the new buyer is legally obligated to honor your lease from the day they purchase the building. Since you're already on the program that means the property passed any necessary inspections, so I don't know why the new owner wouldn't want to keep getting that government check. The tricky part about such programs is getting the property through the necessary inspections to get it going in the first place. Once it's on, it's easy.

The landlord is completely within his rights to put this property up for sale. Read your lease if you're concerned about the property being shown, etc. Typically they'd just have to give you the appropriate notice. Also, don't know how large the building is, but it's customary for a buyer of an apartment building to just view a sampling of apartments, not every single one. So they may not even show your unit.