I'm going to build a pergola in the garden which will mean attaching a few joists (150 x 50) to a building.

It's an old building constructed from very soft Norfolk Red bricks.

How would I connect my joists to the building, it would need to look neat as it will be on show, so I assume this would rule out joist hangers.

Many thanks.

You will need to bolt a bearer timber to the wall and rest the joist on this or better still notch them into it

i. flash your timber ledger with a cover flashing.
2. 2"x4" section timber will do for ledger and joists.
3. connect the ledger with say:Fischer FAZ11 Thrubolts 8mmx95mm or similar.
4. See Simpson catalog for joist hangers for solid joists. You should use hangers for safety/high winds. They can be almost concealed/painted.
5. Use hangers to connect your posts to your rim joists, and your joists to your ledger.

The OP does not want to use ugly hangers, and we have been building without them for a few centuries now

Bolt the timber plate to the wall with a 50mm x 50mm batten screwed to lower edge of plate, you will then only need to cut out 50mm x 50mm from the bearers, skew nail or screw bearers to plate.