3/8 6:30 AM PT -- A judge set Alvarado's bail at $30,000 cash or $75,000 bond.

A guy who's clearly Taylor Swift-obsessed is in custody after going full cat burglar, allegedly ... he was busted after climbing onto her roof and kicking in a door, and it's not his first time on the premises.

Law enforcement tells TMZ ... Roger Alvarado managed to get on the roof of Taylor's Tribeca pad early Thursday morning -- around 2 AM -- but once he busted down a door to gain entry her alarm system sounded. We're told Taylor's security team reacted immediately, calling cops to the scene.

Alvarado was arrested on the scene, which has gotta feel like deja vu for him. NYPD nabbed him last April at this same residence. You might recall, this is the guy who actually took a shower in Taylor's pad before he was busted last year.

In December, he pled guilty to attempted burglary and criminal contempt. He was sentenced to 6 months in jail -- and was credited with time served since he'd been behind bars since the original April arrest -- and 5 years probation.

Taylor was not home at the time, and Alvarado is still in custody.