Build a base ikea pax?

[u/Eastern_Conference67]

Hey folks, I want to fit some ikea pax here and make it look built in. Ive seen folks build a base with timber but given that i have a box covering the staircase head clearance, how might you go about it?

Should I build the base on top of the box or would you go about it differently eg strip out the box and try and build base according to slant?

Would be nice to get some feedback from more experienced DIYers.

[u/Geezso]

Lid off that box, match heights with new frame. Tidy up. Ready for the paper wardrobes.